1. Relating to gravel:
* Descriptive of something made of or resembling gravel: A gravelly road, a gravelly beach, a gravelly voice (meaning rough and grating).
* Containing gravel: The soil is gravelly.
2. Describing a voice:
* Rough and grating: He has a gravelly voice, probably from years of smoking.
The context of the sentence will usually make it clear which meaning is intended.