diacritic (adj.)

before vowels, di-, word-forming element meaning "through, in different directions, between," also often merely intensive, "thoroughly, entirely," from Greek dia "through; throughout," probably cognate with bi- and related to duo "two" (from PIE root *dwo- "two") with a base sense of "twice."

Proto-Indo-European root meaning "to sieve," thus "discriminate, distinguish."

It forms all or part of: ascertain; certain; concern; concert; crime; criminal; crisis; critic; criterion; decree; diacritic; discern; disconcert; discreet; discriminate; endocrine; excrement; excrete; garble; hypocrisy; incertitude; recrement; recriminate; riddle (n.2) "coarse sieve;" secret; secretary.

It is the hypothetical source of/evidence for its existence is provided by: Greek krinein "to separate, decide, judge," krinesthai "to explain;" Latin cribrum "sieve," crimen "judgment, crime," cernere "to sift, distinguish, separate;" Old Irish criathar, Old Welsh cruitr "sieve;" Middle Irish crich "border, boundary;" Old English hriddel "sieve."