early 15c., in physiology, "absorb into and make part of the body," from Latin assimilatus, past participle of assimilare, assimulare "to make like, copy, imitate, assume the form of; feign, pretend," from assimilated form of ad "to" (see ad-) + simulare "make similar," from similis "like, resembling, of the same kind" (see similar).
Meaning "make alike, cause to resemble," and intransitive sense "become incorporated into" are from 1620s. In linguistics, "bring into accordance or agreement in speech," from 1854. Related: Assimilated; assimilating.
updated on April 21, 2017