mid-14c., declaren, "explain, interpret, make clear;" late 14c., "make known by words, state explicitly, proclaim, announce," from Old French declarer "explain, elucidate," or directly from Latin declarare "make clear, reveal, disclose, announce," from de-, here perhaps an intensive prefix (see de-) + clarare "to clarify," from clarus "clear" (see clear (adj.)).
From mid-15c. as "assert, affirm." Intransitive sense "make known one's thoughts or intentions" is by 1840. Related: Declared; declaring.
Old English utlagian "to banish, proscribe, declare an outlaw; to deprive (someone) of the benefits and protections of the law," from utlaga "an outlaw" (see outlaw (n.)). Related: Outlawed; outlawing.
mid-15c., protesten, "to declare or state formally or solemnly, bear witness or testimony to," from Old French protester and directly from Latin protestari "declare publicly, testify, protest" (see protest (n.)). Original sense preserved in to protest one's innocence. The meaning "make a solemn or formal declaration (often in writing) in condemnation of an act or measure, proposed or accomplished," is from c. 1600. The word's association with marches and rallies arose in 20c. Related: Protested; protesting.
1660s, "declare guilty of a crime;" 1670s, "censure, hold up to blame," from Latin criminatus, past participle of criminare "to accuse of a crime," from crimen (genitive criminis) "crime" (see crime). Related: Crimination (1580s).
early 14c., professen, "to take a vow" (in a religious order), a back-formation from profession or else from Medieval Latin professare, from professus "avowed," literally "having declared publicly," past participle of Latin profiteri "declare openly, testify voluntarily, acknowledge, make public statement of," from pro- "forth" (from PIE root *per- (1) "forward") + fateri (past participle fassus) "acknowledge, confess" (akin to fari "to speak," from PIE root *bha- (2) "to speak, tell, say").
The meaning "declare openly" is recorded from 1520s, "a direct borrowing of the sense from Latin" [Barnhart]. Related: Professed; professing.