Synonyms for Extreme:

adj.

abysmal (adjective)
profound.
agonizing (adjective)
violent.
all (adjective)
utmost, uttermost.
almighty (adjective)
awful.
deep (adjective)
grave.
different (adjective)
unusual.
edge (adjective)
coastal, peripheral, brim, Rimming, ringing, marginal, fringe, border, edge, boundary.
extreme (adjective)
rabid, immoderate, strict, furthermost, uttermost, supreme, intemperate, remarkable, improper, last, outmost, maximum, fanatical, sheer, preposterous, final, drastic, irrational, outrageous, acute, top, unusual, nonsensical, unreasonable, fabulous, inordinate, extravagant, excessive, ultimate, outermost, radical, intense, exaggerated, farthest, desperate, absolute, unconventional, gross, imprudent, highest, utmost, overkill, flagrant, severe, dire.
improper (adjective)
undue.
limiting (adjective)
limiting, Restraining, Terminating, edge, utmost, zenith, constraining, maximum, bounding, restricting, confining.
offensive (adjective)
outrageous.
overenthusiastic (adjective)
fanatical.
severe (adjective)
severe, almighty.
sharp (adjective)
sharp.
summit (adjective)
maximum, crowning, top, topmost, pinnacle, highest, apex, Headmost, Culminating, tip, Capping, zenith, acme, peak, summit, loftiest, uppermost.

adv.

farthest (adverb)
farthest, uttermost.

n.

notable, unique, final, last, remarkable, odd, ultimate, unusual, farthest, exotic, surprising, offbeat, out of the ordinary, special. furthermost, outermost, outmost, profound, grave, serious, farthermost, rigorous, awful, furthest, dire. inaccessible, outlying, remote, supreme, lonely, unsurpassable, better, transcendent, apart, isolated, away. facet, overabundant, overmuch, aspect, factor, undue, nature, peculiarity, feature, excess, quality, property, component. negation, the contrary, concern, fanatic, opposition, obverse, revolutionary, the converse, balance, antithesis, politics, opposite, the reverse, pole.

Other synonyms:

gross, fantastic, outmost, overabundant, irrational, far-out, childish, ultra, unsurpassable, nonsensical, rigorous, perverse, absurd, imprudent, irresponsible, wrong, overmuch. dire, profound, transcendent, supreme, far, outermost, hysterical. acute, grave. awful, revolutionary. ultimate. fanatic. excessive
extravagant, exorbitant, intemperate.
fanatic
fanatical.
fanatical
rabid.
great
almighty.
immoderate
inordinate, immoderate, unreasonable.
intense
violent.
unconventional
way out.

Usage examples for extreme

  1. I am putting extreme cases. – Frank H. Nelson of Cincinnati by Warren C. Herrick
  2. It is hard to form an idea of the extreme care with which this was done. – The Hunters of the Ozark by Edward S. Ellis
  3. In 1596 Burghley, in extreme old age, was a factor no longer to be taken into much consideration. – Raleigh by Edmund Gosse