Stories We Like: A Guide to the Comma
early 14c., "make illustrious, make known," from Old French clarifiier "clarify, make clear, explain" (12c.), from Late Latin clarificare "to make clear," also "to glorify," from Latin clarificus "brilliant," from clarus "clear, distinct" (see clear (adj.)) + root of facere "to make, do" (see factitious).
Meaning "make clear, purify" is from early 15c. in English; intransitive sense of "grow or become clear" is from 1590s. Figurative sense of "to free from obscurity" is from 1823. Related: Clarified; clarifying.