Synonyms for Flail:

n.

punch, bludgeon, smack, stun, thump, beat up, HIT, batter. move, kick, bend, reach out, spread, stretch, extend, strike, attack, close, fold your arms/hands, open, wave. chisel, file, chase, chop, card, cut, drill, crimp, chip away. lawn mower, shovel, hoe, mower, fork, scythe, shears, rake, hose. flail (noun)
lam, thresh, thrash.
thrash (noun)
swing, beat.

v.

beat, strike (verb)
batter, HIT, thrash, smack.
contact (verb)
lam, thresh, thrash.
motion (verb)
thresh.

Other synonyms:

lawn mower, shears, scythe, mower. chip away, HIT, hoe. chisel, beat. shovel. chase, crimp, chop. punch. rake. fork, file. drill. card. thresh
thresh.
Other relevant words:
file, move, smack, shovel, thump, card, strike, batter, crimp, beat, wave, cut, hoe, punch, thrash, HIT, chase.