Irritable, getting dry in a little sun (5)
I believe the answer is:
ratty
'irritable' is the definition.
(thesaurus)
'dry in a little sun' is the wordplay.
'dry' becomes 'tt' (abbreviation for teetotal).
'in' indicates putting letters inside.
'a little sun' becomes 'ray' (as in a ray of sunshine).
'tt' placed into 'ray' is 'RATTY'.
'getting' is the link.
(Other definitions for ratty that I've seen before include "with pests" , "Short-tempered" , "his friend being a dangerous driver" , "Waspish" , "water vole, literally" .)