often thero-, word-forming element meaning "beast," from Greek thēr "wild beast, beast of prey," from PIE root *ghwer- "wild beast." Also therio-, from Greek thērion "wild animal, hunted animal."
word-forming element meaning "horn, horn-like part," from Latinized form of Greek keras (genitive keratos) "horn of an animal; horn as a substance," from PIE root *ker- (1) "horn, head."
before vowels pneum-, word-forming element meaning "lung," from Greek pneumōn "lung," altered (probably by influence of pnein "to breathe") from pleumōn (which was an alternative form in Attic), literally "floater," probably cognate with Latin pulmo "lung(s)," from PIE root *pleu- "to flow." The notion perhaps is from the fact that, when thrown into a pot of water, lungs of a slaughtered animal float, while the heart, liver, etc., do not (compare Middle English lights "the lungs," literally "the light (in weight) organs"). Greek pneumōn also meant "jellyfish, medusa," "perhaps from its rhythmical pulsation, as if breathing" [Thompson].