ḱrey-
“to sieve, to separate, to distinguish”Sieve, separate, distinguish
A PIE verbal root meaning "to sieve, to separate, to distinguish," continued in Greek krī́nein (κρίνειν, "to separate, to judge, to decide"), whence crisis, critic, criterion, and crime; and in Latin cernere ("to sift, to distinguish"), whence certain, concern, discern, discriminate, and secret.
Discussion
The root *ḱrey- ("to sieve, to separate") is reconstructed from Greek krī́nein (κρίνειν, "to separate, to judge, to decide"), Latin cernere ("to sift, to distinguish, to perceive"), Old Irish criathar ("sieve"), Welsh crwydr ("sieve"), and Lithuanian kríjoti ("to sieve"). Pokorny (IEW 945–946) and Rix (LIV² s.v. *krey-) confirm the reconstruction.
Greek krī́nein (κρίνειν, "to separate, to judge") produced one of the richest vocabulary families in Western intellectual history. Krísis (κρίσις, "separation, decision, judgment") gave crisis — a point of decision or turning point. Kritḗs (κριτής, "judge") gave critic and critical. Kritḗrion (κριτήριον, "standard of judgment") gave criterion. The compound hupokritḗs (ὑποκριτής, "one who answers, an actor") gave hypocrite.
Latin cernere ("to sift, to distinguish, to perceive") generated a parallel family: certus ("decided, certain") gave certain and certify; discernere ("to separate, to distinguish") gave discern and discriminate; sēcernere ("to separate apart") gave secrete and secret (literally "separated, set apart"); and conc̄ernere gave concern.
The derivative crīmen (Latin, from Greek) originally meant "judgment, accusation" before narrowing to "offence, crime" — the thing judged. English crime, criminal, and incriminate descend from this branch.
The semantic development from physical sieving to intellectual judgment illustrates one of the most important metaphorical patterns in IE vocabulary: concrete separation actions becoming abstract cognitive operations.
Notes
gsc-gap: source of "crisis", "critic", "criterion", "crime", "discriminate", "secret", "certain"
Laryngeal Analysis
No laryngeal.
Ablaut
Full grade *ḱrey-, zero grade *ḱri-.