[dredmorbius]

Critical, from critic:

1580s, "one who passes judgment," from Middle French critique (14c.), from Latin criticus "a judge, literary critic," from Greek kritikos "able to make judgments," from krinein "to separate, decide" (from PIE root krei- "to sieve," thus "discriminate, distinguish"). Meaning "one who judges merits of books, plays, etc." is from c. 1600. The English word always had overtones of "censurer, faultfinder."*

http://www.etymonline.com/index.php?term=critic&allowed_in_f...

That is, you literally cannot use the term "critical thinking" without employing metaphor.