Here’s a fun word. It started out as a corruption and misspelling of another word and then gained use with a meaning derived from the etymological construction of the word as it had been misspelled!
lit. A helper, an assistant.
As first used in 1647, only a bad spelling of AGITATOR, originating with soldiers familiar with adjutants (often pronounced and occas. written AGITANT) and the adjutors of 1642. But writers unacquainted with the function of these ‘agitators,’ mistook adjutator (understood in its etymological sense) for the proper form. Hence, it has been occas. used in the general sense of ‘helper.’