Measure discharge about the incomplete understanding (7)
I believe the answer is:
empathy
'understanding' is the definition.
(I've seen this before)
'measure discharge about the incomplete' is the wordplay.
'measure' becomes 'em' (em is a kind of measure).
'discharge' becomes 'pay' ().
'about' means one lot of letters goes inside another.
'incomplete' means to remove the last letter.
'the' with its last letter taken away is 'th'.
'pay' going around 'th' is 'pathy'.
'em'+'pathy'='EMPATHY'
(Other definitions for empathy that I've seen before include "Ability to identify with another's feelings" , "Fellow feeling" , "Intuitive fellow-feeling" , "Sharing experiences" , "Ability to share another's feelings" .)