Tear for the right purpose (4)
I believe the answer is:
rend
'tear' is the definition.
(I know that rend is a more specific form of the action tear)
'for the right purpose' is the wordplay.
'the right' suggests the final letters (the letter on the right of the word).
'purpose' becomes 'end' (both can mean a goal).
The last letter of 'for' is 'r'.
'r'+'end'='REND'
(Other definitions for rend that I've seen before include "Tear to pieces" , "split" , "Cleave" , "Tear apart roughly" , "Tear violently" .)