English learnt painfully, never to be forgotten (7)
I believe the answer is:
eternal
'never to be forgotten' is the definition.
(I've seen this in another clue)
'english learnt painfully' is the wordplay.
'english' becomes 'e' (abbreviation).
'painfully' indicates anagramming the letters (letters get injured).
'learnt' anagrammed gives 'ternal'.
'e'+'ternal'='ETERNAL'
(Other definitions for eternal that I've seen before include "Seemingly without end" , "Valid for all time" , "Never-ending, existing always" , "abiding" , "Imperishable" .)