-id²

Forming nouns.

Either French ‑ide, via Latin ‑idis, or Latin ‑ides, in both cases derived from Greek.

This ending forms the names of some plants whose family name ends in ‑aceae (orchid, family Orchidaceae); of some animals whose taxonomic name ends in ‑idae (felid, a mammal of the cat family, Felidae; noctuid, a moth of the family Noctuidae); or of plants or animals in classes whose name ends in ‑ida (arachnid, a member of the class Arachnida).

It is also used to form the names of structural constituents in biology (chromatid, each of the two thread-like strands into which a chromosome divides during cell division; plasmid, a genetic structure in a cell that can replicate independently of the chromosomes).

In astronomy it can denote a meteor in a shower radiating from a specified constellation (Geminids, from Gemini; Leonids, from Leo); a cepheid is a variable star like the first one observed, Delta Cephei.

The ending can also indicate a member of a dynasty or family (Abbasid, a member of a dynasty of caliphs who ruled in Baghdad from 750 to 1258; Sassanid, a member of a dynasty that ruled Persia from the early 3rd century AD until the Arab Muslim conquest of 651).

See also ‑oid.