There are 599 twelve-letter words containing A and 2M, https://www.bestwordlist.com/c/a/3/12letterwordswithamm.htm
ABNORMALISMS ACADEMICISMS ACCOMMODABLE ACCOMMODATED ACCOMMODATES
ACCOMMODATOR ACHROMATISMS ADMONISHMENT AEROEMBOLISM AGRAMMATICAL
AGROSTEMMATA ALLOMORPHISM AMALGAMATING AMALGAMATION AMALGAMATIVE
AMALGAMATORS AMBULANCEMAN AMBULANCEMEN AMERCIAMENTS AMETABOLISMS
AMMONIATIONS AMMUNITIONED AMORTISEMENT AMORTIZEMENT AMPEROMETRIC
AMPHETAMINES AMPHISTOMOUS AMPHITHECIUM ANAGRAMMATIC ANAMORPHISMS
ANEMOMETRIES ANIMALCULISM ANTIFEMINISM ANTIHUMANISM ANTIJAMMINGS
ANTIMNEMONIC ARITHMOMANIA ARITHMOMETER ARMAMENTARIA ASTIGMATISMS
ASYMMETRICAL ASYMPTOMATIC ATTEMPERMENT AUTOIMMUNITY AUTOMOBILISM
AUTOMORPHISM AXISYMMETRIC BACKGAMMONED BACKSWIMMERS BICAMERALISM
BIMETALLISMS BLAMESTORMED BOHEMIANISMS BOMBARDMENTS BREASTSUMMER
CALCEAMENTUM CALLIGRAMMES CAMPIMETRIES CAMPODEIFORM CENTIGRAMMES
CHAMBERMAIDS CHASMOGAMIES CHASMOGAMOUS CHROMATICISM CHROMATOGRAM
CHROMONEMATA CLAMJAMFRIES CLAMJAMPHRIE CLAMMINESSES CLOMIPRAMINE
COCKAMAMIEST COLUMBARIUMS COMANAGEMENT COMMANDEERED COMMANDERIES
COMMANDINGLY COMMANDMENTS COMMEASURING COMMEMORABLE COMMEMORATED
COMMEMORATES COMMEMORATOR COMMENDATION COMMENDATORS COMMENDATORY
COMMENSALISM COMMENSALITY COMMENSURATE COMMENTARIAL COMMENTARIAT
COMMENTARIES COMMENTATING COMMENTATION COMMENTATORS COMMERCIALLY
COMMINATIONS COMMISERABLE COMMISERATED COMMISERATES COMMISERATOR
COMMISSAIRES COMMISSARIAL COMMISSARIAT COMMISSARIES COMMISSIONAL
COMMITTEEMAN COMMONALTIES COMMONPLACED COMMONPLACES COMMONWEALTH
COMMUNALISED COMMUNALISER COMMUNALISES COMMUNALISMS COMMUNALISTS
COMMUNALIZED COMMUNALIZER COMMUNALIZES COMMUNICABLE COMMUNICABLY
COMMUNICANTS COMMUNICATED COMMUNICATEE COMMUNICATES COMMUNICATOR
COMMUNITAIRE COMMUTATIONS COMPARTMENTS COMPLEMENTAL COMPLIMENTAL
COMPRIMARIOS CONSUMMATELY CONSUMMATING CONSUMMATION CONSUMMATIVE
CONSUMMATORS CONSUMMATORY CRASSAMENTUM CREMATIONISM CREMATORIUMS
CUPRAMMONIUM CYTOMEMBRANE DARMSTADTIUM DEMAGOGUISMS DEMIMONDAINE
DEMONIACISMS DEMONIANISMS DEMONOMANIAS DEPROGRAMMED DEPROGRAMMER
DEPROGRAMMES DIAGRAMMABLE DIAGRAMMATIC DIAMAGNETISM DICHROMATISM
DISARMAMENTS DISMASTMENTS DRAMATICISMS DURALUMINIUM DYNAMOMETERS
DYNAMOMETRIC ELEMENTALISM EMBARQUEMENT EMBATTLEMENT EMBLAZONMENT
EMBLEMATICAL EMBLEMATISED EMBLEMATISES EMBLEMATISTS EMBLEMATIZED
EMBLEMATIZES EMBRACEMENTS EMBRANCHMENT EMMENAGOGUES EMOLUMENTARY
EMOTIONALISM EMPANELMENTS EMPLACEMENTS EMPYREUMATIC ENDAMAGEMENT
ENFRAMEMENTS ENJAMBEMENTS ENTHYMEMATIC ENTRAMMELING ENTRAMMELLED
EPIGRAMMATIC EPITHALAMIUM EUDAEMONISMS EUDAIMONISMS FLAMMABILITY
FLAMMIFEROUS FLAMMULATION FLIMFLAMMERS FLIMFLAMMERY FLIMFLAMMING
FUNAMBULISMS GAMESMANSHIP GAMESOMENESS GAMMERSTANGS GAMOTROPISMS
GEMMOLOGICAL GEMMULATIONS GEOMAGNETISM GOURMANDISMS GRAMMALOGUES
GRAMMATICISE GRAMMATICISM GRAMMATICIZE GRAMMATOLOGY GYMNATORIUMS
HAEMACHROMES HAEMANGIOMAS HAEMATEMESES HAEMATEMESIS HAEMOCHROMES
HAEMODYNAMIC HAMMERCLOTHS HAMMERHEADED HAMMERSTONES HARMONIUMIST
HARMONOGRAMS HARMONOMETER HECTOGRAMMES HELIANTHEMUM HELLGRAMMITE
HELMSMANSHIP HEMANGIOMATA HEMODYNAMICS HEXAGRAMMOID HIEROGRAMMAT
HOMEOTHERMAL HOMOLOGUMENA HOMOPLASMIES HOMOTHALLISM IMMACULACIES
IMMACULATELY IMMANENTISMS IMMANENTISTS IMMATERIALLY IMMATURENESS
IMMATURITIES IMMEASURABLE IMMEASURABLY IMMEDIATISMS IMMEMORIALLY
IMMENSURABLE IMMETHODICAL IMMIGRANCIES IMMIGRATIONS IMMISERATING
IMMISERATION IMMODERACIES IMMODERATELY IMMODERATION IMMORALITIES
IMMORTALISED IMMORTALISER IMMORTALISES IMMORTALIZED IMMORTALIZER
IMMORTALIZES IMMOVABILITY IMMUNISATION IMMUNIZATION IMMUNOASSAYS
IMMUTABILITY IMPANELMENTS IMPEACHMENTS IMPEDIMENTAL IMPERIALISMS
IMPERMANENCE IMPERMANENCY IMPOSTHUMATE IMPOSTUMATED IMPOSTUMATES
INCOMMUTABLE INCOMMUTABLY INFLAMMABLES INFLAMMATION INFLAMMATORY
INSTAGRAMMED JACKHAMMERED KATZENJAMMER LAMMERGEIERS LAMMERGEYERS
LAMPADEDROMY LAMPADOMANCY LYMPHANGIOMA LYMPHOMATOID LYMPHOMATOUS
MACADAMISERS MACADAMISING MACADAMIZERS MACADAMIZING MACROCLIMATE
MACROGAMETES MADEMOISELLE MAGISTERIUMS MAGNETOMETER MAGNETOMETRY
MAILGRAMMING MAIMEDNESSES MAINSTREAMED MAINTOPMASTS MAISTERDOMES
MALAPROPISMS MALFORMATION MALIMPRINTED MALTREATMENT MAMILLATIONS
MAMMALOGICAL MAMMALOGISTS MAMMECTOMIES MAMMILLARIAS MAMMILLATION
MAMMILLIFORM MAMMOGRAPHIC MANAGEMENTAL MANDARINISMS MANOMETRICAL
MANORIALISMS MANUMISSIONS MARCATISSIMO MARCONIGRAMS MARGINALISMS
MARIMBAPHONE MARKSMANSHIP MARSHMALLOWS MARSHMALLOWY MARTINETISMS
MASTECTOMIES MASTERMINDED MATCHMAKINGS MATCHMARKING MATERIALISMS
MATERNALISMS MATHEMATICAL MATHEMATISED MATHEMATISES MATHEMATIZED
MATHEMATIZES MAXIMISATION MAXIMIZATION MAYSTERDOMES MEALYMOUTHED
MEASUREMENTS MECAMYLAMINE MEDIAEVALISM MEDICAMENTAL MEDICAMENTED
MEDIEVALISMS MEGALOMANIAC MEGALOMANIAS MEGASTARDOMS MEGAVITAMINS
MELODRAMATIC MEMBRANOUSLY MEMORABILITY MEMORIALISED MEMORIALISER
MEMORIALISES MEMORIALISTS MEMORIALIZED MEMORIALIZER MEMORIALIZES
MEMORISATION MEMORIZATION MENINGIOMATA MEPROBAMATES MERCANTILISM
MERCENARISMS MERCURIALISM MERISTEMATIC MERRYMAKINGS MESMERICALLY
MESOAMERICAN MESOGASTRIUM MESOGNATHISM MESOTHELIOMA METABOLOMICS
METACHRONISM METACOMPUTER METAGNATHISM METAMATERIAL METAMORPHISM
METAMORPHIST METAMORPHOSE METAMORPHOUS METASOMATISM METEMPIRICAL
METEOROGRAMS METHANAMIDES METHANOMETER METHENAMINES METHYLAMINES
METRONOMICAL MICROAMPERES MICROANATOMY MICROCLIMATE MICROGAMETES
MICROMACHINE MICROMANAGED MICROMANAGER MICROMANAGES MICROPAYMENT
MICROPROGRAM MICROTOMICAL MIDSHIPMATES MILLENARISMS MILLESIMALLY
MILLIAMPERES MILLIGRAMMES MILLILAMBERT MIMEOGRAPHED MIMOGRAPHERS
MIMOGRAPHIES MINIMALISTIC MINIMISATION MINIMIZATION MISALIGNMENT
MISALLOTMENT MISASSEMBLED MISASSEMBLES MISDEMEANANT MISDEMEANING
MISDEMEANORS MISDEMEANOUR MISEMPHASISE MISEMPHASIZE MISERABILISM
MISERABLISMS MISESTIMATED MISESTIMATES MISFORMATION MISINFORMANT
MISMARRIAGES MISMATCHMENT MISMEASURING MISPLACEMENT MISPROGRAMED
MISSTATEMENT MISSUMMATION MISTREATMENT MITHRIDATISM MNEMONICALLY
MOCKUMENTARY MOMENTANEOUS MONASTICISMS MONEYMAKINGS MONOCHROMASY
MONOCHROMATE MONOCHROMATS MONODRAMATIC MONOFILAMENT MONOGAMISTIC
MONOGAMOUSLY MONOGRAMMERS MONOGRAMMING MONOMANIACAL MONOMETALLIC
MONOMETRICAL MONOMYARIANS MONOTHALAMIC MONUMENTALLY MOVIEMAKINGS
MUCKAMUCKING MULTICHAMBER MULTIMEGATON MULTINOMIALS MULTINOMINAL
MULTIVITAMIN MUNICIPALISM MURMURATIONS MYCETOMATOUS MYCODOMATIUM
MYCOPLASMATA MYOFILAMENTS MYTHOMANIACS MYXEDEMATOUS NEONOMIANISM
NINNYHAMMERS NOCTAMBULISM NONALUMINIUM NONCOMMITTAL NONFLAMMABLE
NONIMMIGRANT NONMAMMALIAN NONMETAMERIC NORMOTHERMIA NOUMENALISMS
NUMISMATISTS NUMMULATIONS NYMPHOMANIAC NYMPHOMANIAS OMMATOPHORES
OMNISHAMBLES OMPHALOMANCY OVERCRAMMING PALUDAMENTUM PAMPELMOOSES
PAMPELMOUSES PANDAEMONIUM PANDEMONIUMS PANSPERMISMS PANTOMIMICAL
PANTOMIMISTS PARAMORPHISM PENTAMERISMS PERMEAMETERS PHONOGRAMMIC
PLASMALEMMAS PLASMODESMAS PLASMOGAMIES PLASMOSOMATA POLYMASTISMS
PRAGMATICISM PRASEODYMIUM PROGRAMMABLE PROGRAMMATIC PROGRAMMINGS
PROGYMNASIUM PROTHALAMIUM PSAMMOPHILES PSAMMOPHYTES PSAMMOPHYTIC
RADIOMIMETIC REAMENDMENTS RECOMMITTALS REMAINDERMAN REMAINDERMEN
REMEMBERABLE REMEMBERABLY REMEMBRANCER REMEMBRANCES REPROGRAMMED
REPROGRAMMES RHABDOMYOMAS RHEUMATISMAL ROMANTICISMS SARCOLEMMATA
SEMIBASEMENT SEMICOMATOSE SEMIDIAMETER SEMIDOMINANT SEMIMETALLIC
SEMIMONASTIC SEMIMYSTICAL SEMIPALMATED SHAMATEURISM SHUNAMITISMS
SLEDGEHAMMER SMALMINESSES SMARMINESSES SOMATOMEDINS SOMATOPLASMS
SOMNAMBULANT SOMNAMBULARY SOMNAMBULATE SOMNAMBULISM SOMNAMBULIST
SPERMAGONIUM SPHYGMOGRAMS STAMMERINGLY STOMATODAEUM SUBMAXIMALLY
SUBMICROGRAM SUMMARISABLE SUMMARIZABLE SUMMERSAULTS SUPREMACISMS
SUPREMATISMS SYMMETALISMS SYMMETALLISM SYMPTOMATISE SYMPTOMATIZE
SYSTEMATISMS TAUTOMERISMS TELECOMMANDS TELEGRAMMING TEMPERAMENTS
TERMITARIUMS TETRAMERISMS TIMBROMANIAC TIMBROMANIAS TIMESTAMPING
TRANSFORMISM TRIGRAMMATIC TRINOMIALISM TRIUMPHALISM UNCOMMERCIAL
UNPROGRAMMED UNTRAMMELLED VERUMONTANUM VOLTAMMETERS WINDJAMMINGS
XERANTHEMUMS XYLOBALSAMUM YELLOWHAMMER ZOOMAGNETISM