-ium

suffix forming nouns denoting esp.:
1 (also -um) names of metallic elements (uranium; tantalum).
2 a region of the body (pericardium; hypogastrium).
3 a biological structure (mycelium; prothallium).
Etymology: from or after L -ium f. Gk -ion

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noun suffix

1. -s [New Latin, perhaps after such words as Latin medium]

a.

(1) : chemical element

sodium

uranium

(2) : chemical radical

ammonium

b. : an ion having a positive charge — in names of complex cations (as those derived from an organic base)

imidazolium [C₃H₄N₂H]⁺

pyridinium

nitrosylium NO⁺

— compare -onium

2. plural -iums also -ia [New Latin, from Latin, from Greek -ion (n. suffix, often of diminutive force)] : small one : mass — especially in biological terms

onchium

pollinium

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a suffix found on nouns borrowed from Latin, esp. 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).

[ < NL, L, neut. suffix]

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-ium /-i-əm/

suffix

1. Forming nouns denoting: a metallic element, as in plutonium

2. A group forming a positive ion, as in ammonium

3. A biological structure, as in conidium

ORIGIN: Latinized form of Gr -ion

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-ium,

suffix. chemical element or radical, as in curium, sodium, ammonium.

╂[< New Latin -ium < Latin -ium, a neuter suffix]

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suffix

1) forming nouns adopted unchanged from Latin (such as alluvium) or based on Latin or Greek words (such as euphonium)

2) (also -um) forming names of metallic elements

cadmium | magnesium

3) denoting a region of the body

pericardium

4) denoting a biological structure

mycelium

•

Origin:

modern Latin in senses 2, 3, and 4, via Latin from Greek -ion

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-ium, suffix Chem.

a. Used to form the names of metallic elements.

The L. names of metals were in -um, e.g. aurum, argentum, ferrum; the names of sodium, potassium, and magnesium, derived from soda, potassa or potash, and magnesia, were given by Davy in 1807, with the derivative form -ium; and although some of the later metals have received names in -um, the general form is in -ium, as in cadmium, iridium, lithium, osmium, palladium, rhodium, titanium, uranium; in conformity with which aluminum has been altered to aluminium. So hydrogen, when theoretically regarded as a metal, has been called hydrogenium; cf. also ammonium.

b. Used to form the names of various protonated, mostly organic, bases, as anilinium, benzenium, ethenium, flavylium, guanidinium, hydrazinium, imidazolium, pyrylium. Cf. -onium.

This usage of the suffix derives from ammonium. For rules governing the application of the suffix see Nomenclature of Organic Chemistry and Nomenclature of Inorganic Chemistry, published by the International Union of Pure and Applied Chemistry.