Cromwell's issue, for instance, on both sides at the Battle of Naseby? (4)
I believe the answer is:
baby
'naseby?' is the definition.
The answer and definition can be both acts as well as being singular nouns.
Perhaps you can see an association between them that I can't see?
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for baby that I've seen before include "Small child" , "Lumbered, left holding this" , "Comparatively small" , "-- Oil; -- boom" , "Very young child" .)