Heavens! Outside the pub looking undernourished! (6)
I believe the answer is:
skinny
'undernourished' is the definition.
(thesaurus)
'heavens outside the pub' is the wordplay.
'heavens' becomes 'sky' (sky is a kind of heavens).
'outside' indicates putting letters inside.
'the pub' becomes 'inn' (an inn is a type of pub).
'sky' going around 'inn' is 'SKINNY'.
'looking' is the link.
This may not be correct. It may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for skinny that I've seen before include "little of substance?" , "Very slim" , "Thin, bony" , "Lacking food" , "Not very well-built" .)