protest (v.)
mid-15c., "to declare or state formally or solemnly," from Old French protester, from Latin protestari "declare publicly, testify, protest" (see protest (n.)). Original sense preserved in to protest one's innocence. Related: Protested; protesting.
protest (n.)
c. 1400, "avowal, pledge, solemn declaration," from Old French protest (Modern French prôtet), from preotester, and directly from Latin protestari "declare publicly, testify, protest," from pro- "forth, before" (from PIE root *per- (1) "forward," hence "in front of, before") + testari "testify," from testis "witness" (see testament).

Meaning "statement of disapproval" first recorded 1751; adjectival sense of "expressing of dissent from, or rejection of, prevailing mores" is from 1953, in reference to U.S. civil rights movement. First record of protest march is from 1959.