The thickness that makes you sit in and refuse to go out (7)
I believe the answer is:
density
'the thickness that makes you sit in' is the definition.
'density' can be an answer for 'the thickness' (I've seen this before). I'm not sure about the rest of the definition.
'refuse to go out' is the wordplay.
I cannot really understand how this works, but
'go' could be 'sit' (sitting is a kind of going) and 'sit' is found in the answer.
'refuse' could be 'deny' (synonyms) and 'deny' is found within the remaining letters.
No letters remain.
This explanation may well be incorrect...
'and' is the link.
Can you help me to learn more?
(Other definitions for density that I've seen before include "Concentration, compactness" , "The compactness of a substance" , "Degree of compactness" , "'Thickness, concentration (7)'" , "Number of items in a given area" .)