Merriam-Webster Collegiate Dictionary - source

 I. noun  Etymology: Middle English sours, from Anglo-French surse spring, ~, from past participle of surdre to rise, spring forth, from Latin surgere — more at surge  Date: 14th century  1.  a. a generative force ; cause  b.  (1) a point of origin or procurement ; beginning  (2) one that initiates ; author; also prototype, model  (3) one that supplies information  2.  a. the point of origin of a stream of water ; fountainhead  b. archaic spring, fount  3. a firsthand document or primary reference work  4. an electrode in a field-effect transistor that supplies the charge carriers for current flow — compare drain, gate  Synonyms: see origin  • ~less adjective  II. transitive verb  (~d; sourcing)  Date: 1957  1. to specify the ~ of (as quoted material)  2. to obtain from a ~ metals ~d from abroad  III. adjective  Date: 1959 of, relating to, or being ~ code a ~ file