not that tears help its suffering at first (4)
I believe the answer is:
this
'not that' is the definition.
(I've seen this before)
'tears help its suffering at first' is the wordplay.
'at first' says to take the initial letters.
The first letters of 'tears help its suffering' is 'THIS'.
(Other definitions for this that I've seen before include "The thing here referred to" , "near thing" , "One particular" , "Demonstrative pronoun" , "The thing under discussion" .)