c. 1300, "completely, quite, entirely, wholly," c. 1300, from clear (adj.) or adverbial use of the adjective in Old French. From early 14c. as "plainly, lucidly;" mid-14c. as "loudly, with distinctness of sound;" late 14c. as "brightly, brilliantly."
late 14c., "not identical, not the same," also "clearly perceptible by sense," past-participle adjective from obsolete distincten (c. 1300) "to distinguish one thing from another; make distinct," from Old French distincter, from Latin distinctus, past participle of distinguere "to separate between, keep separate, mark off" (see distinguish). Meaning "plain and intelligible to the mind" is from c. 1600. Related: Distinctness.
1540s, " of or pertaining to logical disputation, relating to the art of reasoning;" see dialectic + -al (1). From 1750 as "of or pertaining to a dialect." From 1788 as "of the nature of philosophical dialectic" (in reference to Kant, later to Hegel and Marx). Related: Dialectally. Dialectical materialism (by 1927) translates Marx's phrase.