Etymology
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-ectomy 

word-forming element meaning "surgical removal," from Latinized form of Greek -ektomia "a cutting out of," from ektemnein "to cut out," from ek "out" (see ex-) + temnein "to cut" (from PIE root *tem- "to cut").

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-phage 

word-forming element meaning "eater," from stem of Greek phagein "to eat," from PIE root *bhag- "to share out, apportion; to get a share."

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-phagous 

word-forming element meaning "eating, feeding on," from Latin -phagus, from Greek -phagos "eater of," from phagein "to eat," literally "to have a share of food," from PIE root *bhag- "to share out, apportion; to get a share."

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oxy- 

word-forming element meaning "sharp, pointed; acid," from Greek oxys "sharp, pungent" (from PIE root *ak- "be sharp, rise (out) to a point, pierce" ). Also used as a combining form of oxygen.

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-fuge 

word-forming element meaning "that which drives away or out," from Modern Latin -fugus, with sense from Latin fugare "to put to flight" (see febrifuge) but form from Latin fugere "to flee" (see fugitive (adj.)).

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-fold 

multiplicative word-forming element attached to numerals, from Old English -feald, Northumbrian -fald, from Proto-Germanic *-falda- (cognates: Old Saxon -fald, Old Frisian -fald, Old Norse -faldr, Dutch -voud, German -falt, Gothic falþs), combining form of *falthan, from PIE *polt-, extended form of root *pel- (2) "to fold."

The same root yielded fold (v.) and perhaps also Greek -ploid, -plos and Latin -plus (see -plus). Native words with it have been crowded out by Latinate double, triple, etc., but it persists in manifold, hundredfold, etc.

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-logy 

word-forming element meaning "a speaking, discourse, treatise, doctrine, theory, science," from Greek -logia (often via French -logie or Medieval Latin -logia), from -log-, combining form of legein "to speak, tell;" thus, "the character or deportment of one who speaks or treats of (a certain subject);" from PIE root *leg- (1) "to collect, gather," with derivatives meaning "to speak (to 'pick out words')." Often via Medieval Latin -logia, French -logie. In philology "love of learning; love of words or discourse," apology, doxology, analogy, trilogy, etc., Greek logos "word, speech, statement, discourse" is directly concerned.

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-in (1)

the adverb in attached to a verb as a word-forming element, by 1960, abstracted from sit-in, which is attested from 1941 in reference to protests and 1937 in reference to labor union actions (which probably was influenced by sit-down strike) but was popularized in reference to civil disobedience protests aimed at segregated lunch counters.

As a word-forming element it was extended first of other types of protests, then by 1965 to any sort of communal gathering (such as love-in, attested by 1967). In labor actions it was perhaps less useful: "a mass of workers calling in sick to absent themselves in protest" was called both a sick-out (1970) and a sick-in (1974).

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-ster 

Old English -istre, from Proto-Germanic *-istrijon, feminine agent suffix used as the equivalent of masculine -ere (see -er (1)). Also used in Middle English to form nouns of action (meaning "a person who ...") without regard for gender.

The genderless agent noun use apparently was a broader application of the original feminine suffix, beginning in the north of England, but linguists disagree over whether this indicates female domination of weaving and baking trades, as represented in surnames such as Webster, Baxter, Brewster, etc. (though modern spinster probably carries an originally female ending).

Also compare whitester "one who bleaches cloth;" kempster (c. 1400; Halliwell has it as kembster) "woman who cleans wool." Chaucer ("Merchant's Tale") has chidester "an angry woman" (the 17c. had scoldster). Also compare Middle English shepster (late 14c.) "dressmaker, female cutter-out," literally "shapester." Sewster "seamstress" (Middle English seuestre, late 13c. as a surname, also used of men) is still in Jonson but was obsolete or provincial after 17c. In Modern English, the suffix has been productive in forming derivative nouns (gamester, roadster, punster, rodster "angler," etc.).

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-s (1)

suffix forming almost all Modern English plural forms of nouns, gradually extended in Middle English as -es from Old English -as, the nominative plural and accusative plural ending of certain "strong" masculine nouns (such as dæg "day," nominative/accusative plural dagas "days"). The commonest Germanic declension, traceable back to the original PIE inflection system, it is also the source of the Dutch -s plurals and (by rhotacism) Scandinavian -r plurals (such as Swedish dagar).

Much more uniform today than originally; Old English also had a numerous category of "weak" nouns that formed their plurals in -an, and other strong nouns that formed plurals with -u. Quirk and Wrenn, in their Old English grammar, estimate that 45 percent of the nouns a student will encounter will be masculine, nearly four-fifths of them with genitive singular -es and nominative/accusative plural in -as. Less than half, but still the largest chunk.

The triumphs of -'s possessives and -s plurals represent common patterns in language: using only a handful of suffixes to do many jobs (such as -ing), and the most common variant squeezing out the competition. To further muddy the waters, it's been extended in slang since 1936 to singulars (such as ducks,sweets,babes) as an affectionate or diminutive suffix.

Old English single-syllable collectives (sheep, folk) as well as weights, measures, and units of time did not use -s. The use of it in these cases began in Middle English, but the older custom is preserved in many traditional dialects (ten pound of butter; more than seven year ago; etc.).

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