Missing plurals

-UM but not -A

Chemical elements: ACTINIUM, ALUMINIUM, AMERICIUM, BARIUM, BERKELIUM, BERYLLIUM, BOHRIUM, CADMIUM, CAESIUM, CALCIUM, CERIUM, CHROMIUM, CURIUM, DUBNIUM, ERBIUM, EUROPIUM, FERMIUM, FRANCIUM, GADOLINIUM, GERMANIUM, HAFNIUM, HASSIUM, HELIUM, HOLMIUM, INDIUM, IRIDIUM, LAWRENCIUM, LUTETIUM, MEITNERIUM, MOLYBDENUM, NEODYMIUM, NEPTUNIUM, NIOBIUM, NOBELIUM, OSMIUM, PLATINUM, PLUTONIUM, POLONIUM, PROMETHIUM, RADIUM, RHENIUM, RHODIUM, RUBIDIUM, RUTHENIUM, SAMARIUM, SCANDIUM, SEABORGIUM, SELENIUM, SODIUM, TANTALUM, TECHNETIUM, TELLURIUM, TERBIUM, THALLIUM, THULIUM, TITANIUM, URANIUM, VANADIUM, YTTERBIUM, YTTRIUM. (Note that some chemical elements do admit plurals, but that's for another article.)

Mass nouns: ALLUVIUM, AVIZANDUM, BDELLIUM, BUNKUM (from Buncombe County in North Carolina, not Latin).

Adjectives: ANTEBELLUM, ANTEPARTUM.

Plants (for some reason, plants often do not admit Latinate plurals even when the root word is Latin): ALLIUM, ALYSSUM, ANTHURIUM, ARUM.

Not Latin: BEGUM (from Urdu), BLUEGUM (compound with GUM, from French gomme), BOOJUM (nonsense word from The Hunting of the Snark), BUBBLEGUM (another GUM compound).

Other: ASYLUM (of Latin origin but plural is still ASYLUMS).

To do

ALARUM (mistake?), ALUM (mistake?),

CALADIUM, CAPSICUM, CARDAMUM, CEMENTUM, CERASTIUM, CHECKSUM, CHETRUM, CHILLUM, COCKALORUM, COLCHICUM, COLISEUM, COLLUVIUM, COLOSSEUM, COLOSTRUM, COLUMBIUM, CONUNDRUM, CORIUM, CORUNDUM, CUM, CYMBIDIUM, DECORUM, DEDENDUM, DELIRIUM, DELPHINIUM, DENTALIUM, DEUTERIUM, DIAZONIUM, DIDYMIUM, DINKUM, DOMINIUM, DORONICUM, DRUM, DUMDUM, DYSPROSIUM, EARDRUM, ELECTRUM, EPICARDIUM, EPIMEDIUM, EPIMYSIUM, EPIPHYLLUM, ERYNGIUM, EUPHONIUM, FACTOTUM, FALCIPARUM, FRAENULUM, FRAENUM, FREEMIUM, FRENULUM, FRENUM, GALBANUM, GALLIUM, GELSEMIUM, GERANIUM, GEUM, GLUM, GUAIACUM, GUM, GYPSUM, HABENDUM, HAHNIUM, HARMONIUM, HELENIUM, HOKUM, HOODLUM, HUMDRUM, HYPERICUM, IMPERIUM, INDECORUM, INFIMUM, JEJUNUM, JOLIOTIUM, JORUM, KETTLEDRUM, KHOUM, KUMKUM, LABARUM, LABDANUM, LABURNUM, LADANUM, LANTHANUM, LAUDANUM, LIGUSTRUM, LINOLEUM, LOCUM, LOMENTUM, LUTECIUM, LYCOPODIUM, MAGNUM, MECONIUM, MEERSCHAUM, MENTUM, MODICUM, MUSEUM, MYOCARDIUM, MYOMETRIUM, NASTURTIUM, NATATORIUM, NEUM, NGULTRUM, NOSTRUM, OAKUM, ODIUM, OLEUM, OLIBANUM, OPIUM, OPOSSUM, OPPROBRIUM, ORICHALCUM, ORIGANUM, PABLUM, PABULUM, PANJANDRUM, PANTOUM, PASPALUM, PENDULUM, PEPLUM, PERIMYSIUM, PETROLATUM, PETROLEUM, PHORMIUM, PLENUM, PLUM, POLYGONUM, POMATUM, POPADUM, POPPADUM, POSSUM, POTASSIUM, PRACTICUM, PRAESIDIUM, PRECORDIUM, PREMIUM, PRESIDIUM, PROTIUM, PSALTERIUM, PSYLLIUM, PUERPERIUM, PYRETHRUM, QUADRIVIUM, QUORUM, RHIZOBIUM, RUM, RUMDUM, SANCTUM, SARGASSUM, SCHTUM, SCRUM, SCUM, SEBUM, SEDUM, SESAMUM, SHTUM, SKOOKUM, SLUM, SOLANUM, SORGHUM, SPHAGNUM, SPLENIUM, SPUTUM, STELLIUM, STEPMUM, STEWBUM, STICKUM, STRAMONIUM, STRUM, STUM, STUMBLEBUM, SUGARPLUM, SUM, SUPREMUM, SWUM, TALCUM, TAPETUM, TECTUM, TEDIUM, TEETOTUM, THRUM, TRIDUUM, TRILLIUM, TRITIUM, TROPAEOLUM, UROPYGIUM, VALLUM, VARIORUM, VELLUM, VERATRUM, VERBASCUM, VIBURNUM, WAMPUM, YESSUM.