1510s, "to combine into one body," from Latin consolidatus, past participle of consolidare "to make solid," from assimilated form of com "with, together" (see con-) + solidare "to make solid," from solidus "firm, whole, undivided, entire," from suffixed form of PIE root *sol- "whole."
Meaning "to make firm or strong" is from 1530s; that of "to form into a solid mass" is from 1650s. Intransitive sense "to grow firm or compact" is from 1620s. Caxton (late 15c.) has consolid (v.), from French consolider. Related: Consolidated; consolidating.