The adjective is хлёсткий ("good at lashing"), the comparative is хлеще (not *хлёще)
It comes from хлестать "to lash" and means "trenchant, scathing, vitriolic".
Note that all these words, Russian and English alike, are metaphors which literally mean "causing damage or pain"
The pattern which is used to form this adjective (verb root + кий) means "good at doing something"
- ловить "to catch" > ловкий "dexterous, cunning" (literally "good catcher")
- ять "to take, to have, to seize" > ёмкий "capacious, concise" (literally "good taker or storer")
- звенеть "to ring" > звонкий "sonorous, resonant"
or "easily affected by something":
- ковать "to forge" > ковкий "malleable"
- плавить "to fuse" > плавкий "fusible"
- пасть "to fall" > падкий "susceptible, prone" (literally "easy to fall for something")