1635, "to strengthen, reinforce," from obsolete Fr.
recruter (17c.), from
recrute, Picardy dialect variant of
recrue "levy," lit. "new growth," from O.Fr.
recreu, pp. of
recreistre "grow or increase again," from
re- "again" +
creistre "to grow," from L.
crescere "to grow" (see
crescent). "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]. Sense of "to enlist new soldiers" is attested from 1655; of student athletes, from 1913. Noun meaning "body of military reinforcements" is attested from 1645 (replacing earlier
recrew, recrue).