formerly critick, 1580s, "one who passes judgment, person skilled in judging merit in some particular class of things," from French critique (14c.), from Latin criticus "a judge, a censor, an estimator," also "grammarian who detects spurious passages in literary work," from Greek kritikos "able to make judgments," from krinein "to separate, decide" (from PIE root *krei- "to sieve," thus "discriminate, distinguish"). The meaning "one who judges merits of books, plays, etc." is from c. 1600. The English word always has had overtones of "censurer, faultfinder, one who judges severely."
To understand how the artist felt, however, is not criticism; criticism is an investigation of what the work is good for. ... Criticism ... is a serious and public function; it shows the race assimilating the individual, dividing the immortal from the mortal part of a soul. [George Santayana, "The Life of Reason," 1906]
A perfect judge will read each work of wit
With the same spirit that its author writ;
[Pope, "An Essay on Criticism," 1709]
For "inferior or incompetent critic" 17c. had criticaster; later generations used criticling, critikin, criticule.