An Etymological Dictionary of Astronomy and Astrophysics

A position with respect to a given or specified base. → energy level.

Etymology (EN): From O.Fr. livel, from L. libella “a balance, level,” diminutive of libra “balance, scale.”

Etymology (PE): Tarâz “level; a level,” from tarâzu “balance, scales,” Mid.Pers. tarâzên-, taraênidan “to weigh,” Proto-Iranian *tarāz-, from *tarā- “balance, scale” ( cf. Skt. tulā- “scales, balance, weight,” from tul- “to weigh, make equal in weight, equal,” tolayati “weighs, balances,” L. tollere “to raise,”
Gk. talanton “balance, weight,” Atlas “the Bearer” of Heaven," Lith. tiltas “bridge;” PIE base telə- “to lift, weigh”) + Av. az- “to convey, conduct, drive,” azaiti drives" (cf. Skt. aj- “to dive, sling,” ájati “drives,” ajirá- “agile, quick,”
Gk. agein “to lead, guide, drive, carry off,” L. agere “to do, set in motion, drive,” from PIE root *ag- “to drive, move,” → act).