Etymology: < post-classical Latin and scientific Latin -idium (formations in which are found from at least the late 18th cent.) and its etymon ancient Greek -ίδιον, diminutive suffix < -ιδ- , stem of nouns in -ις (see -id suffix2) + -ιον , diminutive suffix, by reanalysis of words where -ιον had been added to noun stems ending in -ιδ- . Compare French -idie (formations in which are found from at least the second half of the 19th cent.). Compare -id suffix5.Recorded earliest in the early 18th cent. in the Greek loan Ophidion n. (with its variant Ophidium , compare the note at that entry), and subsequently in loans < scientific Latin from the second half of the 18th cent., e.g. Ascidium n., cymbidium n., Oncidium n., venidium n. (all genus names), peridium n., pyxidium n., sporidium n. (all denoting parts of organisms). Formations within English are found from the first half of the 19th cent., apparently earliest in oophoridium n., slightly later in meconidium n. Chiefly combining with first elements ultimately of Greek origin, although compare favellidium n., pistillidium n., venidium n., whose first elements are of Latin origin.
This is a new entry (OED Third Edition, November 2010; most recently modified version published online June 2021).