Glass one rolls over and over again (7)
I believe the answer is:
tumbler
'glass' is the definition.
(tumbler is a kind of glass)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for tumbler that I've seen before include "vessel" , "A large glass" , "Constantly dropping" , "Glass for whisky" , "A drop from a bar may occupy this" .)