Item of clothing stolen by boy or dog (8)
I believe the answer is:
labrador
'dog' is the definition.
(I've seen this before)
'item of clothing stolen by boy or' is the wordplay.
'item of clothing' becomes 'bra' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'stolen by' indicates putting letters inside (inserted letters are taken or stolen).
'boy' becomes 'lad' (informal term for boy).
'bra' put into 'lad' is 'labrad'.
'labrad'+'or'='LABRADOR'
Can you help me to learn more?
(Other definitions for labrador that I've seen before include "Canadian peninsula - dog" , "Breed of retriever" , "Breed of gun dog" , "Canadian region and dog-breed" , "Bar a lord from Canada" .)