Riff

google

ref

1930s: perhaps an abbreviation of refrain2.

wiktionary

ref

Uncertain. Perhaps a clipping of riffle, or an alteration of refrain.

From Middle English *rif (found only in midrif), from Old English hrif(“the belly; womb”), from Proto-West Germanic *hrif, from Proto-Germanic *hrefaz(“body; torso; belly”), from Proto-Indo-European *krep-(“body”). Doublet of corpus.

etymonline

ref

riff (n.)

"a repeated melodic phrase in jazz," 1935 (but said to have been used by musicians since c. 1917), of uncertain origin, perhaps a shortened form of riffle, or altered from refrain. The verb is attested by 1942, from the noun. Also in transferred or extended use (by 1970). Related: Riffed; riffing.