1520s, "to be, exist in a permanent state as a body composed of parts," from French consister (14c.) or directly from Latin consistere "to stand firm, take a standing position, stop, halt," from assimilated form of com "with, together" (see con-) + sistere "to place," causative of stare "to stand, be standing" (from PIE root *sta- "to stand, make or be firm").
From 1560s, with of, as "be composed, be made up." From 1630s as "be consistent." Related: Consisted; consisting.