-ium

(chemistry) Used to form the names of metal elements, after the style of early-named elements, as well as the isotopes of hydrogen.

(chemistry) Used to form the temporary systematic element name of a metallic or nonmetallic element which is postulated to exist, or which has been newly synthesized and has not yet been assigned a permanent name.

(by extension, humorous) Appended to common words to create scientific-sounding or humorous-sounding fictional substance names.

Used to form the name of an aggregation or mass of something, such as biological tissue: for example, epithelium, pollinium. Words so formed often form their plural with -ia.

Used to indicate the setting where a given activity is carried out: for example, auditorium, colloquium, gymnasium, natatorium, planetarium, podium, sanatorium, stadium. Words so formed often take -a for the plural.

(pharmacology) Used to form names of quaternary ammonium compounds used as neuromuscular blocking agents, cholinergic agents, anticholinergic agents, antibacterials/antiseptics, or other agents.