- forming Modern Latin names for chemical elements: sodium
- forming the names of certain positive ions: ammonium, carbonium
- forming the names of certain biological structures: conidium, syncytium
Origin of -iumModern Latin from L, ending of certain neuter nouns
Chemical element or group: californium.
Origin of -iumNew Latin -ium neuter n. suff. from Greek -ion
- Used to form the names of metal elements, after the style of early-named elements, as well as the isotopes of hydrogen.
- By extension, appended to common words to create scientific-sounding or humorous-sounding fictional substance names.
- Used to indicate the setting where a given activity is carried out: gymnasium, auditorium, stadium, colloquium, planetarium, podium, sanatorium. Words so formed often take "-a" for the plural.
From Latin -um (“neuter singular morphological suffix”), based on Latin terms for metals, such as ferrum.