Computer modeller and designer (5)
I believe the answer is:
quant
'computer modeller' is the definition.
The definition suggests a singular noun which matches the answer.
'and designer' is the wordplay.
I cannot really understand how this works, but
'and' could be 'n' (common abbreviation for 'and') and 'n' is found in the answer.
The remaining letters 'quat' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for quant that I've seen before include "fashion designer" , "Mary - - , designer" , "Flat-ended punting or jumping pole" .)