word-forming element meaning "air, atmosphere; gases," in 20c. use with reference to aircraft or aviation, from Greek aēr (genitive aeros) "air, lower atmosphere" (see air (n.1)).
before vowels pyel-, medical word-forming element used from mid-19c. in forming medical terms, from Greek pyelos "oblong trough, bathing-tub," a word of uncertain etymology, taken in modern scientific use for "pelvis."
word-forming element in words of Greek origin meaning "outer, outside, outer part," used from mid-19c. in scientific words (such as exoskeleton), from Greek exō (adv.) "outside," related to ex (prep.) "out of" (see ex-).
word-forming element meaning "of or pertaining to skin," from Greek dermat-, from derma "(flayed) skin, leather," from PIE root *der- "to split, flay, peel," with derivatives referring to skin and leather. The shortened form derm- was used from mid-19c. but is considered incorrect.
word-forming element, used from mid-19c. (first in Eocene) in compound words formed by earth-scientists, and meaning "characterized by the earliest appearance of," from Greek ēōs "dawn, morning, daybreak," also the name of the goddess of the morning, from PIE root *aus- (1) "to shine," especially of the dawn. Piltdown Man, before exposed as a fraud, was known as Eoanthropus.
