Ulster, perhaps, has seashore lacking sun (4)
I believe the answer is:
coat
'ulster perhaps' is the definition.
(ulster is a kind of coat)
'seashore lacking sun' is the wordplay.
'seashore' becomes 'coast' ('coast' can be a synonym of 'seashore').
'lacking' indicates named letters should be taken away.
'sun' becomes 's'.
'coast' with 's' taken away is 'COAT'.
'has' is the link.
(Other definitions for coat that I've seen before include "Jacket" , "Overgarment" , "Warm outerwear" , "blanket" , "Layer of paint" .)