Swine -- dull person, it's said? (4)
I believe the answer is:
boar
'swine' is the definition.
(I've seen this before)
'dull person it's said?' is the wordplay.
'dull person' becomes 'bore' (I've seen this before).
'it's said?' indicates a 'sounds like' (homophone) clue.
'bore' sounds like 'BOAR'.
(Other definitions for boar that I've seen before include "Wild animal, sounds like drill" , "A male pig, sounds tedious" , "A wild male pig" , "Sow's mate" , "Uncastrated male hog" .)