early 15c., "to disturb, trouble," from Middle French soliciter, from Latin solicitare "to disturb, rouse," from sollicitus "agitated," from sollus "whole, entire" + citus "aroused," past participle of ciere "shake, excite, set in motion" (see cite). Related: Solicited; soliciting.
Meaning "to further (business affairs)" evolved mid-15c. from Middle French sense of "manage affairs." The sexual sense (often in reference to prostitutes) is attested from 1701, probably from a merger of the business sense and an earlier sense of "to court or beg the favor of" (a woman), attested from 1590s.