wisp (plural wisps) 1  A small bundle, as of straw or other like substance; any slender, flexible structure or group. A wisp of smoke rose from the candle for a few moments after he blew it out. 2  A whisk, or small broom. 3  A will o' the wisp, or ignis fatuus. Tennyson the wisp that flickers where no foot can tread.