Clear something viscous that's blocked crack (7)
I believe the answer is:
starlit
'clear' is the definition.
Both the answer and definition are adjectives. Maybe they are linked in a way I don't understand?
'something viscous that's blocked crack' is the wordplay.
I cannot really understand how this works, but
'something' could be 'it' (I've seen this in other clues) and 'it' is present in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for starlit that I've seen before include "Illuminated at night (including a newspaper)" , "Illuminated by the night sky" , "romantic setting" .)