"to make white, turn pale," c.1400, from Old French blanchir "to whiten, wash," from blanc "white" (11c.; see blank (adj.)). Originally "to remove the hull of (almonds, etc.) by soaking." Intransitive sense of "to turn white" is from 1768. Related: Blanched; blanching.
"to start back, turn aside," 1570s, variant of blench. Related: Blanched; blanching.