Numnah

[Rihanna]

a felt of [sheepskin] pad placed between a [horses] back and the saddle to prevent chafing
a word used in the 2008 Spelling Bee which was confused with [numnut].

[Merna]

A pad, typically made of sheepskin or foam, which is placed under a saddle.

[Merna]

Numnah in Horse Racing. Soft material that is shaped like a saddle. Placed under the saddle to absorb sweat and make it more comfortable for the horse.