late 14c., "having no deficiency, wanting no part or element; perfect in kind or quality; finished, ended, concluded," from Old French complet "full," or directly from Latin completus, past participle of complere "to fill up, complete the number of (a legion, etc.)," transferred to "fulfill, finish (a task)," from com-, here probably as an intensive prefix (see com-), + plere "to fill" (from PIE root *pele- (1) "to fill").
late 14c., "make complete, bring to an end, supply what is lacking; fulfill, accomplish," from complete (adj.) and probably in part from Latin completus. Related: Completed; completing.
"completing or tending to complete," 1670s, from Late Latin completivus "serving to fill up," from past-participle stem of complere "to fill up" (see complete (adj.)).
the last canonical service of the day, early 13c., cumplie, compelin, from Old French complie (12c.), from Medieval Latin completa, from Latin completa (hora), from completus (see complete (adj.)); with unetymological -n-. So called because the service usually completes the religious exercises of the day. Originally it was said after the evening meal and before retiring to bed, but in later medieval times it shifted to immediately after vespers.
"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.
*pelə-, Proto-Indo-European root meaning "to fill," with derivatives referring to abundance and multitude.
It forms all or part of: accomplish; complete; compliment; comply; depletion; expletive; fele; fill; folk; full (adj.); gefilte fish; hoi polloi; implement; manipulation; nonplus; plebe; plebeian; plebiscite; pleiotropy; Pleistocene; plenary; plenitude; plenty; plenum; plenipotentiary; pleo-; pleonasm; plethora; Pliocene; pluperfect; plural; pluri-; plus; Pollux; poly-; polyamorous; polyandrous; polyclinic; polydactyl; polydipsia; Polydorus; polyethylene; polyglot; polygon; polygraph; polygyny; polyhedron; polyhistor; polymath; polymer; polymorphous; Polynesia; polyp; Polyphemus; polyphony; polysemy; polysyllabic; polytheism; replenish; replete; supply; surplus; volkslied.
It is the hypothetical source of/evidence for its existence is provided by: Sanskrit purvi "much," prayah "mostly;" Avestan perena-, Old Persian paru "much;" Greek polys "much, many," plethos "people, multitude, great number," ploutos "wealth;" Latin plus "more," plenus "full;" Lithuanian pilus "full, abundant;" Old Church Slavonic plunu; Gothic filu "much," Old Norse fjöl-, Old English fela, feola "much, many;" Old English folgian; Old Irish lan, Welsh llawn "full;" Old Irish il, Welsh elu "much."