late 14c., poinaunt, "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 sense of "sharp to the taste" is now obsolete. The word contains an etymological double-reverse. Latin pungere is from the same root as Latin pugnus "fist," and represents a Latin metathesis of -n- and -g- that was reversed in French.