Thoroughbred (8)
'thoroughbred' is the definition.
(I know that thoroughbred can be written as pedigree)
This is all the clue.
(Other definitions for pedigree that I've seen before include "List of ancestors" , "Breeding; descent" , "Line of decent or ancestry" , "Pure lineage" , "(Distinguished) lineage" .)
(Other definitions for racehorse that I've seen before include "hope for better?" , "Arab possibly" , "Which a jockey rides" , "Competitive beast" , "Steeplechaser, maybe" .)