Jolly lot with very big drink container? (7)
I believe the answer is:
thermos
'container?' is the definition.
(thermos is a kind of container)
'jolly lot with very big drink' is the wordplay.
I cannot quite understand how this works, but
'jolly' could be 'rm' (jolly can mean a Royal Marine) and 'rm' is found within the answer.
'big' could be 'os' (abbreviation for oversize) and 'os' is found within the answer.
'drink' could be 'the' (I have seen 'French drink' mean 'the' so perhaps 'drink' could also mean 'the') and 'the' is found within the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for thermos that I've seen before include "Vacuum flask for mothers" , "Flask trade mark" , "Heat-retaining flask for mothers" , "Container to retain heat" .)