type of small, light vessel, generally with two masts and rigged like a schooner but capable of being propelled by oars, 1540s, from French pinace (earlier spinace, 15c., from Old French espinace, Modern French péniche; also attested as Anglo-Latin spinachium (mid-14c.)); a word of unknown origin.
The French word perhaps is from Italian pinaccia or Spanish pinaza, so called for being built of pine wood, from pino "pine tree; ship" (Latin pinus "pine tree" also had a secondary sense of "ship, vessel"). But variations in early forms makes this uncertain. In old slang also "a woman," especially "a mistress, a prostitute" (1560s).