One who pushes a principle or measure to extremes; an extremist; a radical; an ultra (noun)
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Use "ultraist" in a sentence
"And when flouted and reproached by smooth and lofty ecclesiastics, as an ultraist and leveler, he explained and justified himself by observing, that he had only done what his office demanded."
"With us, if between two authors the most remote resemblance of idea or expression can be detected, straightway some ultraist stickler for originality -- some Poe -- shrieks out, 'Some body must be a thief!' and forthwith, all along the highways of reviewdom, is sent up the hue and cry: 'Stop thief! stop thief!'"
"If a man be an ultraist for insisting upon nothing but his rights, with a willingness to compromise even these upon any fair and reasonable terms, without a total abandonment, then I am an ultraist."