Used as the past participle of the verb "untread", functioning adjectivally.
Definitions
Past participle of the verb "untread". He had long since untrodden the path back to safety.
Used attributively to describe something that has not been walked on, e.g. "untrodden snow".
Definitions
Not walked on; pristine, untraveled. The climbers reached a field of untrodden snow near the summit.