An Etymological Dictionary of Astronomy and Astrophysics

Farthest from the center or middle; outermost; exceeding the bounds of moderation. → extreme adaptive optics; → extreme HB star; → extreme horizontal branch star; → extreme infrared; → extreme mass ratio inspiral; → extreme ultraviolet; → extremely metal-poor star.

Etymology (EN): From L. extremus “outermost, utmost,” superlative of exterus, “outer,” comparative of ex “out of,” → ex-.

Etymology (PE): Ostom “outermost, utmost” (Av. (ustəma- “outermost, highest, ultimate”),
superlative of ost “out,” → ex-, + -tom superlative suffix, from Mid.Pers. -tom (xwaštom “most pleasant,” nevaktom “best,” wattom “worst”), from O.Pers. -tama- (fratama- “first, front”); Av. -təma- (amavastəma- “strongest,” hubaiδitəma- “most sweet-scented,” baēšazyôtəma- “most healing,” fratəma- “first, front”); cf. Skt. tama-.