His pudding includes an unexpected ingredient! (4)
I believe the answer is:
spud
'an unexpected ingredient' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe there's a link between them I don't understand?
'his pudding includes' is the wordplay.
'includes' indicates a hidden word.
'SPUD' is hidden in the letters of 'his pudding'.
Can you help me to learn more?
(Other definitions for spud that I've seen before include "one's eyed" , "The humble colloquial potato" , "The popular potato" , "Commoner's King Edward?" , "Vegetable" .)