Sheepish bishop's abandoned bull, say (5)
I believe the answer is:
ovine
'sheepish' is the definition.
(I've seen this before)
'bishop's abandoned bull say' is the wordplay.
'bishop' becomes 'B' (abbreviation used in chess).
'abandoned' indicates named letters should be taken away.
'bull say' becomes 'bovine' (bull is a type of bovine animal).
'bovine' with 'b' removed is 'OVINE'.
(Other definitions for ovine that I've seen before include "Like the Cheviots" , "1/6 = 2/3 of 28 [SHEEPISH" , "Relating to sheep" , "like a mug" , "Sheep-like" .)