THESAURUS
flatten
align, assimilate to, balance, beat down, bend, blow down, break, break down, bring down, bulldoze, burn down, cast down, chop down, conquer, crush, cut down, dab, damp, demolish, disentangle, down, drag, dress, dub, equalize, equilibrize, even, extend, fell, floor, flush, grade, grease, ground, harmonize, harrow, homogenize, humble, knock, knock down, knock out, knock over, lay, lay down, lay flat, lay level, lay low, lay out, level, lubricate, make uniform, master, mow, mow down, normalize, oil, override, plane, planish, plaster, press out, prostrate, pull down, put down, put straight, quell, rase, raze, rectify, reduce, regularize, regulate, ride down, roll, roll flat, set straight, shave, sit up, smash, smooth, smooth down, smooth out, smoothen, stabilize, stand up, standardize, steamroll, steamroller, stereotype, straighten, straighten out, straighten up, subdue, subjugate, suppress, symmetrize, take down, tear down, throw down, trample down, trample underfoot, tread underfoot, unbend, uncurl, uniformize, unkink, unsnarl, vanquish
ROGET THESAURUS
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Horizontality
VB
be horizontal, lie, recline, couch, lie down, lie flat, lie prostrate, sprawl, loll, sit down, render horizontal, lay down, lay out, level,
flatten, prostrate, knock down, floor, fell.
Flatness
VB
render flat,
flatten, level.