Passages coated with brown, sticky stuff beginning to dry, becoming stuck-up (6-5)
I believe the answer is:
toffee-nosed
'stuck-up' is the definition.
(I've seen this before)
'passages coated with brown sticky stuff beginning to dry' is the wordplay.
I cannot really understand how this works, but
'stuff' could be 'toffee' (I have seen 'Chewy stuff' mean 'toffee' so perhaps 'stuff' could also mean 'toffee') and 'toffee' is found in the answer.
The remaining letters 'nosed' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
'becoming' acts as a link.
Can you help me to learn more?
(Other definitions for toffee-nosed that I've seen before include "superior?" , "Stuck-up" , "Snobbish, patronising" , "Supercilious (with a sticky hooter?)" .)