Cavity the driller droned on and on about? (8)
I believe the answer is:
borehole
'on about?' is the definition.
I can't judge whether this defines the answer.
'cavity the driller droned on' is the wordplay.
I cannot quite understand how this works, but
'cavity' could be 'hole' (hole is a kind of cavity) and 'hole' is found within the answer.
'on' could be 're' ('on' can be mean 'with reference to') and 're' is found within the answer.
The remaining letters 'bo' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
'and' acts as a link.
Can you help me to learn more?
(Other definitions for borehole that I've seen before include "Deep excavation to find water" , "Passage made by a drill, for exploratory purposes" , "(A) deep drilling for oil, water" , "It's made to locate water or oil" , "An excavation to reach groundwater" .)