Singer needing one in support (5)
I believe the answer is:
basis
'support' is the definition.
(I've seen this before)
'singer needing one in' is the wordplay.
'singer' becomes 'bass' (bass is a kind of singer).
'needing one' becomes 'i' (I am not sure about this - if you are sure you should believe this answer much more).
'in' indicates putting letters inside.
'bass' going around 'i' is 'BASIS'.
Can you help me to learn more?
(Other definitions for basis that I've seen before include "Reason" , "Principle on which a theory is founded" , "Underlying support for a theory" , "grounds" , "First principle" .)