IPA: /ˈrʌfˌraɪdə/
KK: /ˈrʌfˌraɪdər/
A person who is skilled at riding horses that are not well trained, or a member of a specific cavalry unit from the Spanish-American War led by Theodore Roosevelt.
The roughriders bravely charged into battle during the Spanish-American War.
Roughrider is formed from "rough" (from Old English *ruh*, meaning uneven or coarse) and "rider" (from Old English *ridan*, meaning to ride). The term originally referred to someone who rides in a rough or rugged manner, often associated with cavalry or adventurous riding.
Think of someone who rides in a 'coarse' or 'uneven' way — 'rough' describes the manner, and 'rider' indicates the person who rides.
No commonly confused words.