An Etymological Dictionary of Astronomy and Astrophysics

A prefix occurring originally in loanwords from L., with the basic meaning “on the far side of, beyond, extremely.”

Etymology (EN): From L. ultra- from ultra (adverb and preposition) “beyond, on the further side,” from ulter, from uls “beyond;” + -ter suffix of comparative adj.; PIE base *al- “besides, other, beyond.”

Etymology (PE): Ultar-, from Mid.Pers. ul “up, upward,” ulêh “upward, above” (Av. ərəδuua- “upright, risen; cf. Skt. ūrdhvá- “high, above, elevated; Gr. orthos “set upright, straight;”
L. arduus “high, steep;” → ortho-)

• -tar suffix forming comparative adjectives (Mid.Pers. -tar; Av. -tara- (masculine); PIE base *-tero).