Classical definition:
有章句曰歌，
无章曲曰谣 — 'a song with set verses is
歌, a song without is
谣'. So
谣 originally meant a chanted, unaccompanied folk song. Combine with
童 'child' →
童谣 nursery rhyme; combine with
言 'speech' →
谣言 rumor (talk that spreads like an unwritten song).
