Etymology
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sacro- 

word-forming element meaning "of or involving the sacrum," the bone at the base of the spine. As in sacro-iliac "pertaining to the sacrum and the ilium."

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sch- 
this letter group can represent five distinct sounds in English; it first was used by Middle English writers to render Old English sc-, a sound now generally pronounced (and spelled) "-sh-." Sometimes it was miswritten for -ch-. It also was taken in from German (schnapps) and Yiddish (schlemiel). In words derived from classical languages, it represents Latin sch-, Greek skh-, but in some of these words the spelling is a restoration and the pronunciation does not follow it (as in schism).
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schm- 
substituted for the initial sound of a word and reduplicated with it to convey derision (as in "Oedipus schmoedipus" in the punchline of the old joke about the Jewish mother and the psychiatrist), 1929, from the numerous Yiddish words that begin with this sound.
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se- 
word-forming element, from Latin se-, collateral form of sed- "without, apart, aside, on one's own," related to sed, Latin reflexive pronoun (accusative and ablative), from PIE *sed-, extended form of root *s(w)e-, pronoun of the third person and reflexive (source also of German sich; see idiom).
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seismo- 
word-forming element meaning "earthquake," from Greek seismos "a shaking, shock; an earthquake," also "an extortion" (compare colloquial shake (someone) down), from seiein "to shake, agitate, sway; to quake, shiver" from PIE root *twei- "to agitate, shake, toss; excite; sparkle" (also source of Sanskrit tvesati "to excite; to be excited, inflame, sparkle," and Avestan words for "fears" and "fright, danger").
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self- 
word forming element indicating "oneself," also "automatic," from Old English use of self (pron.) in compounds, such as selfbana "suicide," selflice "self-love, pride, vanity, egotism," selfwill "free will."
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semi- 

before vowels sem-, word-forming element meaning "half, part, partly; partial, imperfect; twice," from Latin semi- "half," from PIE *semi- "half" (source also of Sanskrit sami "half," Greek hēmi- "half," Old English sam-, Gothic sami- "half").

Old English cognate sam- was used in such compounds as samhal "poor health," literally "half-whole;" samsoden "half-cooked," figuratively "stupid" (compare half-baked); samcucu "half-dead," literally "half-alive;" and the last survivor of the group, sandblind "dim-sighted" (q.v.). Common in Latin (as in semi-gravis "half-drunk," semi-hora "half hour," semi-mortuus "half-dead," semi-nudus "half-naked," semi-vir "half-man, hermaphrodite"). The Latin-derived form in English has been active in forming native words since 15c.

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semi-demi- 
word-forming element meaning "sixty-fourth part," 1660s; see semi- + demi-.
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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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