Another interesting etymology.
The original meaning for this word as a verb was:
1.a. trans. To rub down or dress (a horse, ass, etc.) with a comb. c1290 S. Eng. Leg. I. 61/251 And selde heo [an ass] is i-coureyd [? i-conreyd] wel.
It evolved 100 years later to:
a. fig. To ‘stroke down’ (a person) with flattery or blandishment. Obs.
c1394 P. Pl. Crede 365 Whou þey curry kinges & her back claweþ.
†a. to curry favel: to use insincere flattery, or unworthy compliance with the humour of another, in order to gain personal advantage. (Cf. CURRY-FAVEL(L n. below.) [ < Old French estriller fauvel (fauveau , fauvain , also torcher fauvel ) to curry the chestnut horse, hence, to employ deceit or hypocrisy, to gloze; compare FAVEL adj. and n.]
a1420 T. HOCCLEVE De Regimine Principum 189 The knyght or squier..but he hide The trouthe and cory favelle, he not the ner is His lordes grace.
b. Later, this phrase was transformed into to curry favour: to seek to win favour, or ingratiate oneself withanother, by officious courtesy or unworthy complaisance.
?1518 A. BARCLAY tr. D. Mancinus Myrrour Good Maners sig. Hv Flatter nat as do some With none, cory fauell.
1557 Bible (Whittingham) Matt. viii. 20 (note) He thoght by this meanes to courry fauour with the worlde.
ˈfavel, adj. and n.Etymology: < Old French fauvel, < fauve fallow-coloured, < Germanic *falwo- : see FALLOW adj.1 and n.2
The Old French word had all the uses found in English, so that there is no ground for treating sense B. 3 as a distinct word, though it is possible that it may have been associated by some Middle English writers with Old French favele idle talk, cajolery < Latin fābella , diminutive of fābula FABLE n. The phrase ‘to curry Favel’, Old French estriller, torcher Fauvel, comes from the Roman de Fauvel (1310), the hero of which is a counterpart of Reynard the Fox (see P. Paris, MSS. Bibl. du Roi I. 306); it has been adopted in German as den fahlen hengst streichen. It is not clear whether before the date of this poem a ‘fallow’ horse was proverbial as the symbol of dishonesty; the same notion is found in German, ‘to ride the fallow horse’ (den fahlen hengst reiten—recorded from 15th cent.) having the sense ‘to play an underhand game, act deceitfully’.
Of a horse: = FALLOW adj.1 and n.2 (The exact colour denoted by the adj. in early use is uncertain.)
1490 CAXTON tr. Foure Sonnes of Aymon (1885) i. 33 There came rydynge a messager vpon a horse fauell.
1. As the proper name of a fallow-coloured horse.