1630s, "to strengthen, reinforce," from French recruter (17c.), from recrute "a levy, a recruit" (see recruit (n.)). Sense of "to enlist new soldiers" is attested from 1650s; of student athletes, from 1913. Related: Recruited; recruiting.
"military reinforcement, one of a newly raised body of troops," 1640s, from recruit (v.), replacing earlier recrew, recrue; or from obsolete French recrute, alteration of recreue "a supply," recrue "a levy of troops" (late 16c.), Picardy or Hainault dialect variant of recrue "a levy, a recruit," literally "new growth," from Old French recreu (12c.), past participle of recreistre "grow or increase again," from re- "again" (see re-) + creistre "to grow," from Latin crescere "to grow" (from PIE root *ker- (2) "to grow"). "The French word first appeared in literary use in gazettes published in Holland, and was disapproved of by French writers in the latter part of the 17th c." [OED]. The French word also is the source of Dutch recruut, German Recrut, Swedish rekryt.