1530s, "of one form," from Middle French uniforme (14c.), from Latin uniformis "having only one form or shape," from uni- "one" (see uni-) + forma "form" (see form (n.)). Related: Uniformly.
"distinctive clothes worn by one group," 1748, from French uniforme, from the adjective (see uniform (adj.)).
1680s, "to make alike," from uniform (adj.). Meaning "to dress in a uniform" is from 1861. Related: Uniformed.