There are 15 12-letter words that end with 'ium'.
| appressorium | archesporium | epithalamium |
| perionychium | spermagonium | quinquennium |
| radiothorium | praseodymium | protactinium |
| prothalamium | pseudopodium | superpremium |
| transuranium | unnilpentium | unnilquadium |
Note: These 15 12-letter words that end with 'ium' are found from the USA & Canada version of the tournament Scrabble word list.
Also see words end with rium, nium, dium, lium, cium, tium, gium, mium, bium, sium, vium, hium, pium, uium, xium, zium.
5-letter words end with 'ium' (4)