Etymology
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potamo- 

word-forming element meaning "river," from Greek potamos "river," perhaps literally "rushing water," from PIE root *pet- "to rush, to fly."

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elytro- 
word-forming element used for "vagina" in medical terms, from Greek elytron, literally "sheath" (see elytra). Related: Elytral.
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phyto- 
word-forming element meaning "plant," from Greek phyton "plant," literally "that which has grown," from phyein "to bring forth, make grow," from PIE root *bheue- "to be, exist, grow."
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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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alti- 
word-forming element meaning "high," sometimes also alto- (in cloud names, etc.), from Latin altus "high," literally "grown tall," from PIE root *al- (2) "to grow, nourish."
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atelo- 

word-forming element meaning "imperfect development or structure," from Greek atelēs "imperfect, incomplete," literally "without an end," from a- "not, without" (see a- (3)) + telos "the end, fulfillment, completion" (see telos).

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semper- 
word-forming element meaning "always, ever," from Latin semper "always, ever, at all times, continuously" (literally "once for all"), from PIE *semper-, from root *sem- (1) "one; as one, together with" + *per- "during, for."
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ligni- 
sometimes ligno-, word-forming element used from late 19c. and meaning "wood," from Latin lignum "wood (for fuel or construction), firewood," from PIE *leg-no-, literally "that which is collected," from root *leg- (1) "to collect, gather." Related: Lignify; lignification.
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omni- 

word-forming element meaning "all," from Latin omni-, combining form of omnis "all, every, the whole, of every kind," a word of unknown origin, perhaps literally "abundant," from *op-ni-, from PIE root *op- "to work, produce in abundance."

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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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