Old English boy holds a number (5)
I believe the answer is:
saxon
'old english' is the definition.
The answer and definition can be both people as well as being singular nouns.
Maybe there's an association between them I don't understand?
'boy holds a number' is the wordplay.
'boy' becomes 'sax'.
'holds a number' becomes 'on' (I can't justify this - if you can you should give a lot more credence to this answer).
'sax'+'on'='SAXON'
Can you help me to learn more?
(Other definitions for saxon that I've seen before include "Germanic conqueror of southern England" , "Germanic invader of England" , "Race of England's rulers before the Conquest" , "dating from the first millennium?" , "Member of Germanic tribe settled in southern England after the Romans" .)