-ium

From Latin -um (“neuter singular morphological suffix”), based on Latin terms for metals such as ferrum (“iron”).

-ium

1. (chemistry) Used to form the names of metal elements, after the style of early-named elements, as well as the isotopes of hydrogen.
2. (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.
3. (by extension, humorous) Appended to common words to create scientific-sounding or humorous-sounding fictional substance names.
   • 1997, Bryan Pfaffenberger, Official Microsoft Internet Explorer 4 book, page 34:

     According to the FAQ, a site's coolness can be attributed to a trace element called coolium.

   • 2007, Jason Lethcoe, Wishing Well, appendix, page ii:

     Stupidium: Exposure to this Element can cause very silly behavior.

   • 2009, Selena Kitt, Quickies, page 91:

     We're at the North Pole, aren't we? Let's just call the new element Santa Clausium!

4. 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.
5. 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.

• appressorium
• basidium
• capillitium
• cephalodium
• conidium
• cystidium
• gongylidium
• isidium
• mycelium
• peridium
• sclerotium
• soredium
• sporangium

• -um
• -ion

• IMU, MUI, Miu, Mui, UIM, imu

-ium

1. -ium

From -ius (suffix forming adjectives): as a nominal suffix (Suffix 1), a substantivisation of its neuter forms; as an adjectival suffix (Suffix 2), regularly declined forms.

• (Classical) IPA^(key): /i.um/, [i.ũ] (stressed on the antepenult)

-ium n (genitive -iī or -ī); second declension

1. Suffix used to form abstract nouns, sometimes denoting offices and groups. May no longer be productive.

   ‎auspex + ‎-ium → ‎auspicium

   ‎dēsīderō + ‎-ium → ‎dēsīderium

   ‎castellum (“castle”) + ‎-ium → ‎castilium (“fortified city”)

2. (New Latin) Suffix appended to form names of chemical elements.

Second declension.

¹Found in older Latin (until the Augustan Age).

-ium

1. nominative neuter singular of -ius
2. accusative masculine singular of -ius
3. accusative neuter singular of -ius
4. vocative neuter singular of -ius

• “-ium” on page 981/3 of the Oxford Latin Dictionary (1st ed., 1968–82)