late 14c., "painful to physical or mental feeling" (of sauce, spice, wine as well as things that affect the feelings), from Old French poignant "sharp, pointed" (13c.), present participle of poindre "to prick, sting," from Latin pungere "to prick, pierce, sting," figuratively, "to vex, grieve, trouble, afflict" (from suffixed form of PIE root *peuk- "to prick"). Related: Poignantly.
The word disguises a linguistics trick-play, a double reverse. Latin pungere is from the same root as Latin pugnus "fist," and represents a metathesis of -n- and -g- that later was reversed in French.