One doing the numbers for OAP from Singapore (6)
I believe the answer is:
singer
'one doing the numbers for oap' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'from singapore' is the wordplay.
I cannot quite see how this works, but
'from' could be 'in' (I've seen this in other clues) and 'in' is present in the answer.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for singer that I've seen before include "Coventry car firm" , "one to celebrate?" , "Make of sewing machine" , "Warbler" , "choirboy?" .)