Etymology
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zoo- 
word-forming element meaning "animal, living being," from Greek zoion "an animal," literally "a living being," from PIE root *gwei- "to live" (source also of Greek bios "life").
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ther- 

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."

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spermato- 
before vowels spermat-, word-forming element meaning "seed, sperm," used from 1880s in scientific compounds, from Greek sperma (genitive spermatos "seed" of an animal or plant; see sperm).
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cerato- 

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."

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kerato- 
before vowels, kerat-, scientific word-forming element meaning "horn, horny," also "cornea of the eye" (see cornea), from Greek keras (genitive keratos) "the horn of an animal; horn as a material," from PIE root *ker- (1) "horn; head."
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bio- 
word-forming element, especially in scientific compounds, meaning "life, life and," or "biology, biology and," or "biological, of or pertaining to living organisms or their constituents," from Greek bios "one's life, course or way of living, lifetime" (as opposed to zoe "animal life, organic life"), from PIE root *gwei- "to live." The correct usage is that in biography, but since c. 1800 in modern science it has been extended to mean "organic life," as zoo-, the better choice, is restricted in modern use to animal, as opposed to plant, life. Both are from the same PIE root. Compare biology.
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histo- 
medical word-forming element, from Greek histos "warp, web," literally "anything set upright," from histasthai "to stand," from PIE root *sta- "to stand, make or be firm." Taken by 19c. medical writers as the best Greek root from which to form terminology for "tissue, structural element of the animal body."
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pneumo- 

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].

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