"grammatical form indicating the function of a verb," 1570s, an alteration of mode (n.1). The grammatical and musical (1590s) usages of it influenced the meaning of mood (n.1) in such phrases as light-hearted mood, but it is worth remembering that the two moods have no etymological relationship. Also used in traditional logic (1560s) as a variant of mode.
flat worm-like animal, 1819, from Modern Latin (1776) noun use of fem. of Late Latin planarius, literally "on level ground" (here used to mean "flat"), from Latin planum, planus "flat, level, even, plain" (from PIE root *pele- (2) "flat; to spread"). Related: Planarian.
"one who yields in combat, one who begs for mercy, one who admits defeat," early 15c., hence "coward, faint-hearted wretch;" from recreant (adj.) and from Old French recreant as a noun, "one who acknowledges defeat, a craven, coward, renegade, traitor, wretch." In English, the sense of "apostate, deserter, villain" is from 1560s.
1590s, "make plain, show clearly," a sense now obsolete, a back-formation from remonstration, or else from Medieval Latin remonstratus, past participle of remonstrare "to demonstrate" (see remonstrance). Meaning "to exhibit or present strong reasons against" an act, measure, etc. is from 1690s. Related: Remonstrated; remonstrating.