Add cubes, maybe derived from small, insignificant number (7)
I believe the answer is:
sweeten
'add cubes maybe' is the definition.
(as in adding sugar cubes)
'small insignificant number' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'insignificant' becomes 'wee'.
'number' becomes 'ten' (ten is a kind of whole number).
's'+'wee'+'ten'='SWEETEN'
'derived from' acts as a link.
(Other definitions for sweeten that I've seen before include "Make fresh" , "pacify!" , "Make more palatable" , "Soften up" , "temper" .)