n. 25B6; noun
the source of the river : SPRING, origin, (well) head, headspring, headwater(s); poetic/literary wellspring.
the source of the rumour : ORIGIN, birthplace, spring, fountainhead, fount, starting point; history, provenance, derivation, root, beginning, genesis, start, rise; author, originator, initiator, inventor; N. Amer. provenience.
a historian uses primary and secondary sources : REFERENCE, authority, informant; document.