Synonyms for Sink:

n.

dwindle, diminish, crater, ewer, pan, shrink. grieve, gutter, get down, feel sorry for someone, ache, pine, drain, mourn, upset yourself, regret. full moon, founder, wax, eclipse, come up, orbit, submerse, go in. come to, enter, come, fulfill, touch, attain, push. cue, cue ball, billiards, pool, baize, frame, bar billiards, cushion, pocket, pitch. dishpan, douche, bidet, mudbath, bath, jacuzzi, better, hot tub, shower, retrograde. down, bunk, curl up, cuddle up, bed down, hunker down, lay, stoop, flop. right, spiral, descend into, escalate, slip into. ruin, darken, destroy, wobble, torpedo, cross up, shatter, break, total, break down, smash, say/wave/kiss goodbye to something, finish, spoil, undo, bankrupt, wrack, help, lose/give up hope, despair, demolish, wash up, give up on, lose heart, wreck. flag, languish, fizzle, weaken, carry, strong, fail, splash, waste, swim. speculate, put in, hedge, save, dig, underwrite, drive, plow into, stab, invest, pay into, thrust, roll over, ram, stick. register, spear, knowledge, soak in, plunge into, impale, plunge in. sell out, resort to, not scruple to do something, perpetrate, commit, compromise yourself/your position, go/run off the rails, transgress. do something of your own accord, do your own thing, be alone in (doing) something, go solo, fend for yourself, stand-alone, mind your own business. basin (noun)
cistern, bathtub, bowl, washtub, basin, tub, tureen, vat, tank.
sink (noun)
bury, drop down, sump, subside, drop, slump, cesspool, dip, lapse, fall off, slide down, pass, cesspit.

v.

be humble or humbled (verb)
debase.
deepen (verb)
deepen.
depress (verb)
debase, decrease, lower, attenuate, depress.
descend (verb)
fall, descend, drop, tumble, come down, plummet, settle, topple, fall down.
deteriorate (verb)
fall apart, decrease, ebb, weaken, decay, slump, get worse, deteriorate, collapse, wither, flag, relapse, atrophy, revert, slip, retrogress, fail, go downhill, degenerate, lapse, wilt, moulder, waste, putrefy, regress, retrograde, dwindle, spoil, downgrade, fade, tergiversate, worsen, decline, slide, dilapidate, wane.
disappear (verb)
flee, melt, disappear, fly, evanesce, hide, go, depart, evaporate, dissolve, vanish.
fall, decrease (verb)
lapse, relapse, diminish, retrogress, wane, collapse, slip.
fall in, go under (verb)
engulf, plummet, plunge, ebb, drown, drive, ram, founder, drop, stoop, wreck, disappear, decline, dig, stick, subside, fall, lay, stab, thrust, descend, immerse, lower, submerge, regress, slump, depress, dip, settle.
immerse (verb)
dunk, inundate, plunge, bathe, engulf, flood, dip, drown, douse, wallow, immerse, submerge.
motion (verb)
dip.

Other synonyms:

pine, give up on, mourn, orbit, invest, get down, pay into, perpetrate, full moon, grieve, eclipse, impale, transgress, despair. gravitate, regret, go in, plow into, darken, submerse, founder, speculate, underwrite, torpedo. stoop, weaken, ram, shatter, nose dive, fail, plunge in, skid, destroy, fizzle, demolish, languish, wax, bankrupt. sell out, roll over, wobble, retrograde, dive, spoil, thrust, spear. hedge, plunge into. dig, come up, ache, smash, stab, undo. put in, finish, waste. pitch. splash. drive. break, stick. bow down
stoop.
descend
get down.
die
break down.
invest
put in.
lower
lower.
push down
depress.
relapse
relapse.
waste
waste.

Usage examples for sink

  1. He lifted his head all the way up and let it sink all the way down, and you still don't know who he is. – Further Foolishness by Stephen Leacock
  2. Moreover, my Snake tells me that we shall not sink at least not all of us. – Allan and the Holy Flower by H. Rider Haggard
  3. You are ready to sink into the earth, but there is no escape. – Old Calabria by Norman Douglas