Home › Words › S › setfastsetfast/ˈsɛtfɑːst/setfast means A tumour on a horse's back.setfast is pronounced /ˈsɛtfɑːst/.EtymologyFrom set + fast.nounA tumour on a horse's back.e.g.“Her brother Clint had bought a horse and saddle off that pastor and there had been a setfast under the blanket nearly the size of a griddle cake.” — 2013, Philipp Meyer, The Son, Simon & Schuster, published 2014, page 8:Definitions & examples from Wiktionary (CC BY-SA 3.0).