word-forming element usually meaning "with, together," from Latin com, archaic form of classical Latin cum "together, together with, in combination," from PIE *kom- "beside, near, by, with" (compare Old English ge-, German ge-). The prefix in Latin sometimes was used as an intensive.

Before vowels and aspirates, it is reduced to co-; before -g-, it is assimilated to cog- or con-; before -l-, assimilated to col-; before -r-, assimilated to cor-; before -c-, -d-, -j-, -n-, -q-, -s-, -t-, and -v-, it is assimilated to con-, which was so frequent that it often was used as the normal form.

*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."

"to bend, yield," late 14c., plien, from Old French plier, earlier pleier "to fold, bend," from Latin plicare "to lay, fold, twist" (from PIE root *plek- "to plait"). Related: Plied; plies; plying.

"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.

1640s, "act of complying; disposition to yield to others," from comply + -ance. Related: Compliancy.

"yielding to desire, ready to accommodate," 1640s, from comply + -ant.