Etymology
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coeno- 

before vowels coen-, word-forming element meaning "common," from Latinized form of Greek koinos "common, public, shared, general, ordinary," from PIE *kom "beside, near, by, with" (see com-).

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pen- 

a Brythonic (Celtic) word for "head;" common in place names in Cornwall and Wales (such as Penzance; see also pendragon and Pennsylvania).

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pt- 

An initial consonant combination common in Greek; the p- typically is silent in English words that have it but pronounced in French, German, etc.

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per- 

word-forming element common in words of French and Latin origin, meaning primarily "through," thus also "throughout; thoroughly; entirely, utterly," from Latin preposition per (see per (prep.)).

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socio- 
word-forming element meaning "social, of society; social and," also "having to do with sociology," from combining form of Latin socius "companion, ally, associate, fellow, sharer," from PIE *sokw-yo-, suffixed form of root *sekw- (1) "to follow." Common in compounds since c. 1880.
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octa- 
before vowels oct-, word-forming element meaning "eight," from Greek okta-, okt-, from PIE *okto(u) "eight" (see eight). The variant form octo- often appears in words taken from Latin, but the Greek form is said to be the more common in English.
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pleio- 

also pleo-, word-forming element meaning "more," from Greek pleiōn "larger, greater in quantity, the more part, very many" (comparative of polys "much"), from PIE *ple- (source also of Latin plere "to fill," plebes, "the populace, the common people;" Greek plēthein "be full," plērēs "full"), possibly a variant of root *pele- (1) "to fill."

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wr- 
common Germanic consonantal combination, especially to start words implying twisting or distortion. Retained in Dutch and Flemish; reduced to -r- in Old High German and Old Norse; represented by vr- in Danish and Swedish; still spelled -wr- in English, but the -w- ceased to be pronounced c. 1450-1700 except in dialects.
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cn- 

initial consonant combination used in Old English (the Clark Hall dictionary has 82 entries under cn-), but not now admitted in speech, the n- only being sounded. In Middle English spelling all were lost or turned to kn-. It also is retained in the spelling of some Latinized words from Greek, where initial kn- was common.

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kn- 
Middle English spelling of a common Germanic consonant-cluster (in Old English it was graphed as cn-; see K). The sound it represented persists in most of the sister languages, but in English it was reduced to "n-" in standard pronunciation by 1750, after about a century of weakening and fading. It was fully voiced in Old and Middle English.
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