a suffix found on nouns borrowed from Latin, especially derivatives of verbs (odium; tedium; colloquium; delirium), deverbal compounds with the initial element denoting the object of the verb (nasturtium), other types of compounds (equilibrium; millennium), and derivatives of personal nouns, often denoting the associated status or office (collegium; consortium; magisterium); -ium, also occurs in scientific coinages on a Latin model, as in names of metallic elements (barium; titanium) and as a Latinization of Gk -ion (pericardium).
Origin
< Neo-Latin,Latin, neuter suffix
British Dictionary definitions for -ium
-ium
suffix
1.
indicating a metallic element: platinum, barium
2.
(in chemistry) indicating groups forming positive ions: ammonium chloride, hydroxonium ion
3.
indicating a biological structure: syncytium
Word Origin
New Latin, from Latin, from Greek -ion, diminutive suffix