There are 655 twelve-letter words containing A, M, 2S and T, https://www.bestwordlist.com/c/a/5/12letterwordswithamsst.htm
ABOLISHMENTS ABSENTEEISMS ABSTEMIOUSLY ACCLIMATISES ACCOMPANISTS
ACHROMATISES ACHROMATISMS ADOPTIANISMS ADOPTIONISMS ADVENTURISMS
AEROTROPISMS AESTHETICISM AGNOSTICISMS AGRITOURISMS AGROTOURISMS
AHISTORICISM ALLOTROPISMS ALMIGHTINESS ALTALTISSIMO AMATEURSHIPS
AMAZONSTONES AMBITIONLESS AMETABOLISMS AMISSIBILITY AMPHISTOMOUS
AMPHISTYLARS ANASTOMOSING ANGIOSTOMOUS ANISOTROPISM ANTIELITISMS
ANTIFASCISMS ANTIMACASSAR ANTIMISSILES ANTIREALISMS ANTONOMASIAS
APOLITICISMS APOSTOLICISM APOTROPAISMS APPEASEMENTS ARTEMISININS
ASCOMYCETOUS ASPHETERISMS ASSEMBLAGIST ASSIMILATING ASSIMILATION
ASSIMILATIVE ASSIMILATORS ASSIMILATORY ASSUAGEMENTS ASSUMABILITY
ASSUMPTIVELY ASTIGMATISMS ASTONISHMENT ASTOUNDMENTS ASTROCOMPASS
ASTROCYTOMAS ASTROMETRIES ASTRONOMISED ASTRONOMISES ASTRONOMIZES
ASTROTOURISM ATHLETICISMS ATMOSPHERICS ATOMISATIONS ATTORNEYISMS
AUTOEROTISMS AUTOSAMPLERS AVITAMINOSES AVITAMINOSIS BARGEMASTERS
BARNSTORMERS BASEMENTLESS BATHMITSVAHS BATSMANSHIPS BIMETALLISMS
BIMETALLISTS BLOODSTREAMS BRAGGARTISMS BREASTSUMMER BULLMASTIFFS
BURGOMASTERS CALLISTEMONS CASHIERMENTS CATHETERISMS CATHOLICISMS
CAUSATIONISM CHARISMATICS CHASTENMENTS CHASTISEMENT CHEMONASTIES
CHEMOTAXISES CHOIRMASTERS CHORUSMASTER CHRISMATIONS CHROMOPLASTS
CLICKSTREAMS CLISTOGAMIES COMMISERATES COMMISSARIAT COMMUNALISTS
COMPARATISTS COMPENSATORS CONSERVATISM CONSUMMATORS CORPORATISMS
CORYBANTISMS COSMETICIANS COSMOLATRIES COSMONAUTICS COSMOPLASTIC
CRASSAMENTUM CREATIANISMS CREATIONISMS CRIMINALISTS CROSSMATCHED
CROSSMATCHES CUSTOMISABLE DEDRAMATISES DELASSEMENTS DEMAGNETISES
DEMIBASTIONS DEMOCRATISES DEMOCRATISTS DEMONSTRATES DEMUTUALISES
DERMATITISES DESAGREMENTS DESPUMATIONS DEUTSCHMARKS DIASTROPHISM
DIATONICISMS DIDACTICISMS DIDACTYLISMS DIPLOMATESES DIPLOMATISES
DIPLOMATISTS DISABLEMENTS DISACCUSTOMS DISAMENITIES DISARMAMENTS
DISBANDMENTS DISCARDMENTS DISMANTLINGS DISMASTMENTS DISMUTATIONS
DISSEMINATED DISSEMINATES DISSEMINATOR DISSIMILATED DISSIMILATES
DISSIMULATED DISSIMULATES DISSIMULATOR DOMESTICATES DRAMATICISMS
DRILLMASTERS DYNASTICISMS DYSRHYTHMIAS EMASCULATORS EMBLEMATISES
EMBLEMATISTS EMPASSIONATE EMULATRESSES ENSLAVEMENTS ENSNAREMENTS
ERGASTOPLASM ESCHEATMENTS ESSENTIALISM ESTRAMAZONES EUDAEMONISTS
EUDAIMONISTS EVANISHMENTS EXTERNALISMS FACSIMILISTS FANTASTICISM
FATHOMLESSLY FAVOURITISMS FISSIPALMATE FORETOPMASTS FRAGMENTISES
FUNAMBULISTS GALIMATIASES GAMMERSTANGS GAMOTROPISMS GANGSTERDOMS
GANGSTERISMS GARNISHMENTS GASTRONOMERS GASTRONOMICS GASTRONOMIES
GASTRONOMIST GASTROTOMIES GLOSSEMATICS GLUTAMINASES GNATHOSTOMES
GONIMOBLASTS GOSSAMERIEST GRANDMASTERS GUESSTIMATED GUESSTIMATES
GUTTURALISMS GYNAECOMASTS HAEMATEMESES HAEMATEMESIS HAEMATOLYSES
HAEMATOLYSIS HAEMOSTASIAS HAEMOSTATICS HALOPHYTISMS HAMMERSTONES
HARMONICISTS HARVESTTIMES HEADMISTRESS HEMATOBLASTS HEXAMETRISES
HEXAMETRISTS HIPPEASTRUMS HIPPODAMISTS HISTAMINASES HOMESTEADERS
HOMOBLASTIES HOMOEOSTASES HOMOEOSTASIS HOMOPLASTIES HOUSEMASTERS
HUNTSMANSHIP HYLOPATHISMS IMITABLENESS IMMANENTISMS IMMANENTISTS
IMMATURENESS IMMEDIATISMS IMMORTALISES IMPASSIONATE IMPASTATIONS
IMPERIALISTS IMPERSONATES IMPOSTUMATES IMPROVISATES INFANTILISMS
INFORMATISES INSECTARIUMS INSEMINATORS INSNAREMENTS INSTALLMENTS
INSTATEMENTS INSTREAMINGS INTIMATENESS ISOLATIONISM ISOMAGNETICS
ISOMETROPIAS ITEMISATIONS JUSTICIALISM LITERARYISMS LOGOMACHISTS
LYMPHOBLASTS MACKINTOSHES MACROCYTOSES MACROCYTOSIS MADRIGALISTS
MAGISTERIUMS MAGISTRACIES MAGNATESHIPS MAGNESSTONES MAIDSERVANTS
MAINTOPMASTS MAINTOPSAILS MAISONNETTES MAISTERDOMES MAJESTICNESS
MALAPERTNESS MALAPROPISTS MALEFACTRESS MALPOSITIONS MAMMALOGISTS
MANDOLINISTS MANGALSUTRAS MANIFESTANTS MANIFESTNESS MARCATISSIMO
MARGINALISTS MARQUESSATES MARQUISETTES MARTINETISMS MASCULINISTS
MASSOTHERAPY MASTECTOMIES MASTERLINESS MASTERPIECES MASTERSINGER
MASTERSTROKE MASTICATIONS MASTURBATORS MATERIALISES MATERIALISMS
MATERIALISTS MATERIALNESS MATERNALISMS MATHEMATISES MATRONLINESS
MATURENESSES MAYSTERDOMES MEADOWSWEETS MEASUREMENTS MEDIATRESSES
MEDIEVALISTS MEGALOBLASTS MEGASTARDOMS MELANOBLASTS MELANOSITIES
MEMORIALISTS MENSURATIONS MESOGASTRIUM MESOGNATHIES MESOGNATHISM
MESOGNATHOUS MESOTHORACES MESOTHORAXES METACARPUSES METAPHORISTS
METAPSYCHICS METASEQUOIAS METASOMATISM METASTASISED METASTASISES
METASTASIZED METASTASIZES METATARSUSES METATHESISED METATHESISES
METATHESIZES METROSEXUALS MIDDENSTEADS MIDSHIPMATES MILITANTNESS
MILQUETOASTS MINIATURISES MINIATURISTS MINICASSETTE MISADJUSTING
MISALLOCATES MISANTHROPES MISANTHROPOS MISBESTOWALS MISCANTHUSES
MISCEGENATES MISCELLANIST MISCHANCIEST MISCITATIONS MISCREATIONS
MISERABILIST MISERABLISTS MISESTIMATED MISESTIMATES MISEVALUATES
MISLOCATIONS MISRELATIONS MISSTATEMENT MISSUMMATION MISTAKENNESS
MISTRANSLATE MISTREADINGS MODERATENESS MOLESTATIONS MONASTICISMS
MONOCRYSTALS MONOLATRISTS MONOTASKINGS MULTIFLASHES MULTITASKERS
MUSCULATIONS MUSCULATURES MUSICALITIES MUSSITATIONS MUTATIONISTS
MUTESSARIFAT MUTUALNESSES MYCOPHAGISTS MYOGRAPHISTS MYSTAGOGUSES
MYSTICALNESS NATIONALISMS NEMATOBLASTS NEOVITALISMS NIMBOSTRATUS
NITROSAMINES NOTAPHILISMS NOUMENALISTS NUMISMATISTS OBSCURANTISM
ONOMASTICONS OPHTHALMISTS ORGANISTRUMS ORIENTALISMS ORNAMENTISTS
OSMOLALITIES OSMOLARITIES OSTEOSARCOMA OSTRACODERMS PANENTHEISMS
PANSPERMISTS PANTOMIMISTS PARABAPTISMS PARAMASTOIDS PARAMETRISES
PASSAMENTING PASSEMENTING PASTORALISMS PATERNALISMS PATRISTICISM
PEDANTICISMS PENTAMERISMS PHAGOCYTISMS PHOTOMOSAICS PHYTOPLASMAS
PLAGIOSTOMES PLASMOSOMATA PLASTOGAMIES PLASTOMETERS POLYAMORISTS
POLYMASTISMS POSTORGASMIC PRAGMATISERS PRESAGEMENTS PRIMATESHIPS
PROGNATHISMS PROTAGONISMS PSAMMOPHYTES RATIONALISMS REACTIONISMS
REASSESSMENT REASSIGNMENT REASSORTMENT REASSUMPTION RELATIONISMS
RELEASEMENTS REMONSTRANTS REMONSTRATES RESTATEMENTS RESTIMULATES
RETRANSFORMS RHEUMATEESES ROMANTICISES ROMANTICISMS ROMANTICISTS
SABERMETRICS SACRAMENTALS SALINOMETERS SALTATIONISM SALTIMBANCOS
SALTIMBOCCAS SALVATIONISM SANCTIMONIES SAPROPHYTISM SARCOMATOSES
SARCOMATOSIS SATELLITIUMS SCAMBAITINGS SCAPEGOATISM SCATTERGRAMS
SCHEMATISING SCHISMATICAL SCHISMATISED SCHISMATISES SCHISMATIZED
SCHISMATIZES SCHISTOSOMAL SCHMALTZIEST SCHOOLMASTER SCITAMINEOUS
SCOUTMASTERS SCYPHISTOMAE SCYPHISTOMAS SEAMSTRESSES SECTARIANISM
SECTIONALISM SEISMONASTIC SEMANTICISTS SEMATOLOGIES SEMIABSTRACT
SEMIBASEMENT SEMICOMATOSE SEMIFINALIST SEMIMONASTIC SEMIMYSTICAL
SEMINALITIES SEMIOTICIANS SEMIPARASITE SEMITRAILERS SENSATIONISM
SEPTICAEMIAS SHAMATEURISM SHOWMANLIEST SHUNAMITISMS SILLIMANITES
SIMILARITIES SIMULCASTING SIMULTANEOUS SIMVASTATINS SITUATIONISM
SLACKTIVISMS SLIPSTREAMED SMALLCLOTHES SMARTWATCHES SOLARIMETERS
SOLMISATIONS SOLMIZATIONS SOMAESTHESIA SOMAESTHESIS SOMAESTHETIC
SOMATOLOGIES SOMATOLOGIST SOMATOMEDINS SOMATOPLASMS SOMATOSTATIN
SOMATOTENSIC SOMATOTONIAS SOMATOTONICS SOMERSAULTED SOMESTHESIAS
SOMNAMBULIST SPASMOLYTICS SPECTROGRAMS SPELAEOTHEMS SPERMAPHYTES
SPERMATHECAS SPIRITUALISM SQUAMOSITIES STABLISHMENT STACTOMETERS
STADIOMETERS STAKHANOVISM STAKTOMETERS STALLMASTERS STANDPATTISM
STARTLEMENTS STEAMFITTERS STEAMINESSES STEAMROLLERS STEATOMATOUS
STEELMAKINGS STEGANOGRAMS STENTMASTERS STEPFAMILIES STERCORANISM
STIGMASTEROL STIGMATISERS STIGMATISING STIGMATIZERS STIMULANCIES
STIMULATIONS STIMULATIVES STOMACHACHES STOMATITIDES STOMATITISES
STONEMASONRY STRABISMICAL STRABISMUSES STRABOMETERS STRABOTOMIES
STREAMLINERS STRETCHMARKS STRIPPAGRAMS SUBBASEMENTS SUBDOMINANTS
SUBFRAGMENTS SUBLIMATIONS SUFFUMIGATES SUMATRIPTANS SUMMERSAULTS
SUPERMARKETS SUPERSTARDOM SUPERSTRATUM SUPREMACISTS SUPREMATISMS
SUPREMATISTS SURBASEMENTS SUSTAINMENTS SYCOPHANTISM SYMMETALISMS
SYMMETALLISM SYMPATHETICS SYMPATHISERS SYMPATHISING SYMPATHIZERS
SYMPTOMATISE SYNAPTOSOMAL SYNAPTOSOMES SYNDACTYLISM SYSTEMATICAL
SYSTEMATISED SYSTEMATISER SYSTEMATISES SYSTEMATISMS SYSTEMATISTS
SYSTEMATIZED SYSTEMATIZER SYSTEMATIZES SYSTEMICALLY TAMEABLENESS
TAMELESSNESS TAPHONOMISTS TASKMISTRESS TAUTOLOGISMS TAUTOMERISMS
TAXIDERMISES TAXIDERMISTS TEETOTALISMS TELEMESSAGES TEMPORALISES
TEMPORALNESS TESTIMONIALS TETRAMERISMS TETRATHEISMS THALASSAEMIA
THALASSAEMIC THALASSEMIAS THALASSEMICS THEATRICISMS THEOMACHISTS
THIRDSTREAMS TIMEPLEASERS TOASTMASTERS TRANSAMINASE TRANSFORMERS
TRANSFORMISM TRANSFORMIST TRANSHUMANTS TRANSMISSION TRANSMISSIVE
TRANSMITTALS TRANSMITTERS TRANSVESTISM TROMBIDIASES TROMBIDIASIS
TROPHOPLASMS TRUCKMASTERS TRYPANOSOMES TYMPANITESES TYMPANITISES
ULTIMATENESS UNSYMPATHIES UNSYSTEMATIC VASECTOMISED VASECTOMISES
VASECTOMIZES VIGILANTISMS VOLUNTARISMS WHARFMASTERS WHATSERNAMES
WHATSHISNAME WHATSISNAMES WHATSITSNAME WHOREMASTERS WRECKMASTERS