declare v.

active word-forming element in English and in many verbs inherited from French and Latin, from Latin de "down, down from, from, off; concerning" (see de), also used as a prefix in Latin, usually meaning "down, off, away, from among, down from," but also "down to the bottom, totally" hence "completely" (intensive or completive), which is its sense in many English words.

As a Latin prefix it also had the function of undoing or reversing a verb's action, and hence it came to be used as a pure privative — "not, do the opposite of, undo" — which is its primary function as a living prefix in English, as in defrost (1895), defuse (1943), de-escalate (1964), etc. In some cases, a reduced form of dis-.

c. 1300, "giving light, shining, luminous;" also "not turbid; transparent, allowing light to pass through; free from impurities; morally pure, guiltless, innocent;" of colors, "bright, pure;" of weather or the sky or sea, "not stormy; mild, fair, not overcast, fully light, free from darkness or clouds;" of the eyes or vision, "clear, keen;" of the voice or sound, "plainly audible, distinct, resonant;" of the mind, "keen-witted, perspicacious;" of words or speech, "readily understood, manifest to the mind, lucid" (an Old English word for this was sweotol "distinct, clear, evident"); of land, "cleared, leveled;" from Old French cler "clear" (of sight and hearing), "light, bright, shining; sparse" (12c., Modern French clair), from Latin clarus "clear, loud," of sounds; figuratively "manifest, plain, evident," in transferred use, of sights, "bright, distinct;" also "illustrious, famous, glorious" (source of Italian chiaro, Spanish claro), from PIE *kle-ro-, from root *kele- (2) "to shout."

The prehistoric sense evolution to light and color involves an identification of the spreading of sound and the spreading of light (compare English loud, used of colors; German hell "clear, bright, shining," of pitch, "distinct, ringing, high").

Also in Middle English "beautiful, magnificent, excellent" (c. 1300); of possession or title, "unrestricted, unconditional, absolute," early 15c. Of complexion, from c. 1300. Sense of "free from encumbrance," later largely nautical, developed c. 1500. Meaning "obvious to the senses" is from 1835. Clear-sighted is from 1580s (clear-eyed is from 1520s); clear-headed is from 1709. For coast is clear see clear (v.).

*kelə-, Proto-Indo-European root meaning "to shout." Perhaps imitative.

It forms all or part of: acclaim; acclamation; Aufklarung; calendar; chiaroscuro; claim; Claire; clairvoyance; clairvoyant; clamor; Clara; claret; clarify; clarinet; clarion; clarity; class; clear; cledonism; conciliate; conciliation; council; declaim; declare; disclaim; ecclesiastic; eclair; exclaim; glair; hale (v.); halyard; intercalate; haul; keelhaul; low (v.); nomenclature; paraclete; proclaim; reclaim; reconcile.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit usakala "cock," literally "dawn-calling;" Latin calare "to announce solemnly, call out," clamare "to cry out, shout, proclaim;" Middle Irish cailech "cock;" Greek kalein "to call," kelados "noise," kledon "report, fame;" Old High German halan "to call;" Old English hlowan "to low, make a noise like a cow;" Lithuanian kalba "language."