Fourpenceworth of history (5)
I believe the answer is:
groat
'history' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'fourpenceworth of' is the wordplay.
I cannot really understand how this works, but
'of' could be 'o' and 'o' is found within the answer.
The remaining letters 'grat' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for groat that I've seen before include "Old coin worth four pence" , "Old English silver coin" , "Old fourpenny coin" , "Old English coin worth four pennies" , "Medieval coin" .)