Etymology
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complement (n.)

late 14c., "means of completing; that which completes; what is needed to complete or fill up," from Old French compliement "accomplishment, fulfillment" (14c., Modern French complément), from Latin complementum "that which fills up or completes," from complere "fill up," from com-, here probably as an intensive prefix (see com-), + plere "to fill" (from PIE root *pele- (1) "to fill").

From c. 1600 as "full quality or number, full amount;" musical sense of "simple interval that completes an octave from another simple interval" is from 1873. In 16c. also having senses which were taken up c. 1650-1725 by compliment.

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complement (v.)

"make complete," 1640s, from complement (n.). Earlier in a now-obsolete sense of "exchange courtesies" (1610s), from complement (n.) in a 16c. sense "that which is added, not as necessary, but as ornamental," now going with compliment. Related: Complemented; complementing.

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cosecant (n.)

in trigonometry, 1706, from co, short for complement, + secant.

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cotangent (n.)

in trigonometry, "the tangent of the complement of a given angle," a contraction of co. tangent, abbreviation of complement + tangent (n.).

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cosine (n.)

in trigonometry, 1630s, contraction of co. sinus, abbreviation of Medieval Latin complementi sinus (see complement + sine). The word was used in Latin c. 1620 by English mathematician Edmund Gunter.

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complementary (adj.)

1620s, "ceremonious" (a sense now obsolete in this spelling of the word), from complement (n.) + -ary. Sense of "forming a complement, mutually completing each other's deficiencies," is attested by 1794, in reference to the calendar of the French Revolution; in reference to colors which in combination produce white light, by 1814. Earlier in the sense "completing, forming a complement" was complemental (c. 1600).

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compliment (n.)

"act or expression of civility, respect, or regard" (or, as Johnson defines it, "An act, or expression of civility, usually understood to include some hypocrisy, and to mean less than it declares"), 1570s, complement, ultimately from Latin complementum "that which fills up or completes" (see complement, which is essentially the same word), the notion being "that which completes the obligations of politeness."

The spelling of this derived sense shifted in English after c. 1650 to compliment, via French compliment (17c.), which is from Italian complimento "expression of respect and civility," from complire "to fill up, finish, suit, compliment," from Vulgar Latin *complire, for Latin complere "to complete" (see complete (adj.)).

By early 19c. the meaning had been extended to "an expression of praise or admiration. Meaning "a present or favor bestowed, a complimentary gift" is from 1722.

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fax (n.)

1948, in reference to the technology, short for facsimile (telegraphy). Meaning "a facsimile transmission" is by 1980. The verb attested by 1970. Related: Faxed; faxing.

Futurists predict that a "fax" terminal in the house or business office may someday complement or even replace the mail-carrier. [Scientific American, 1972]
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repletion (n.)

late 14c., replecioun, "eating or drinking to excess," also "state of being replete, fact or condition of being filled up," from Old French repletion, replection (early 14c.) and directly from Late Latin repletionem (nominative repletio) "a filling up, complement," noun of action from past-participle stem of replere "to fill" (see replete). Meaning 

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Rebecca 

fem. proper name, biblical wife of Isaac, mother of Jacob and Esau, from Late Latin Rebecca, from Greek Rhebekka, from Hebrew Ribhqeh, literally "connection" (compare ribhqah "team"), from Semitic base r-b-q "to tie, couple, join" (compare Arabic rabaqa "he tied fast"). Rebekah, the form of the name in the Authorized Version, was taken as the name of a society of women (founded 1851 in Indiana, U.S.) as a complement to the Odd Fellows.

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