The sense of ‘mockery, ridicule’ is considered a derivation of the sense ‘upper leg’ (cf. FEW 7,429b and Gdf 7,483b (‘exagération, mauvaise plaisanterie’)).
s.
1pathol.horsesbony tumour or growth on the leg of a horse:
(
MS: s.xii1/4
) Si cist souros ci est venuz par dialbe
[sic] inchantesun, tollet l’en Deus par sa magne resurectium
82.1
2mockery, ridicule:
(
s.xiii2; MS: s.xiv2/4
) Suros ne fait a porter ke beal s'en put deliverer
31
suros (s.xii1/4)