'riding-horse' originates from Old English components: 'riding' (from Old English 'rīdan') and 'horse' (from Old English 'hors'), where 'rīdan' meant 'to ride' and 'hors' meant 'horse'.

'riding-horse' developed as a straightforward compound in Middle English, combining forms like 'rīding'/'ridin' and 'hors' and eventually appearing in modern English as 'riding-horse' or the unhyphenated 'riding horse'.

Initially it referred simply to a horse for riding, and over time the meaning has remained largely consistent as 'a horse used as a mount'.