mid-13c. (trans.), c.1300 (intrans.), from O.Fr. assembler (11c.), from L. assimulare "to make like, think like," later "to gather together," from ad- "to" + simulare "to make like" (see simulation). In 14c. it also was a euphemism for "to couple sexually." Assemble together
is redundant. Meaning "to put parts together" in manufacturing is from 1852.