Set tough English examination at last (6)
I believe the answer is:
harden
'set' is the definition.
(I've seen this before)
'tough english examination at last' is the wordplay.
'tough' becomes 'hard' (similar in meaning).
'english' becomes 'e' (abbreviation).
'at last' says to take the final letters.
The final letter of 'examination' is 'n'.
'hard'+'e'+'n'='HARDEN'
(Other definitions for harden that I've seen before include "Grow more firm" , "Set; become tougher" , "Become firm or tough" , "Become firm and solid" , "Steel oneself" .)