IPA: /ʌnˈrɪdən/
KK: /ʌnˈrɪdən/
Describing something that has not been ridden, often used in reference to horses or vehicles.
The horse stood in the field, unridden and free.
Unridden → It is formed from "un-" (meaning not) and "ridden" (the past participle of "ride", which comes from Old English "ridan", meaning to ride). The word "unridden" means not having been ridden or not having been used for riding.
Think of 'not' ('un-') having been 'ridden' — that's why unridden means something that hasn't been ridden.