An Etymological Dictionary of Astronomy and Astrophysics

A quantity which is independent of the coordinate system. For example the vector product of two vectors is an invariant since it depends only on the magnitude of the two vectors and the angle between them.

Etymology (EN): From negation prefix → in- + variant, from L. variantem (nom. varians), pr.p. of variare “to change,” from varius “varied, different, spotted.”

Etymology (PE): Nâvartâ, from negation prefix nâ-, → in-, + vartâ adj., from vartidan, variant of gardidan, gaštan
“to change; to turn,” Mid.Pers. vartitan;
Av. varət- “to turn, revolve;” cf. Skt. vrt- “to turn, roll,” vartate “it turns round, rolls;” L. vertere “to turn;” O.H.G. werden “to become;” PIE base *wer- “to turn, bend.”