1590s, "state of standing still; firmness," from Middle French consistence (Modern French consistance) "a standing fast," from Medieval Latin consistentia, literally "a standing together," from Latin consistentem (nominative consistens), present participle of 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."
Meaning "coherence, solidity, state or degree of density" is recorded from 1620s.