An Etymological Dictionary of Astronomy and Astrophysics

A prefix meaning eight.

Etymology (EN): From L. octo, Gk. okto, cognate with Pers. hašt, as below.

Skt. asta, Goth. ahtau, O.E. eahta (see eight).

Etymology (PE): Hašt “eight,” from Mid.Pers. hašt, O.Pers.*aštahva- “eighth;” Av. ašta; cf. Skt. astā; Ossetic ast; (Buddhist) Sogdian ‘št; Gk. okto, L. octo (Fr. huit; Sp. ocho);
P.Gmc. *akhto(u) (O.E. eahta, æhta, E. eight, O.N. atta, Ger. acht, Goth. ahtau); PIE base *oktô(u).
Octa-, oct, loaned Gk. forms, as above.