Express pleasure in almost virtuous manner at last (4)
I believe the answer is:
purr
'express pleasure' is the definition.
(I've seen this before)
'almost virtuous manner at last' is the wordplay.
'almost' means to remove the last letter (almost the whole word is kept).
'virtuous' becomes 'pure' (synonyms).
'at last' says to take the final letters.
The final letter of 'manner' is 'r'.
'pure' with its last letter taken off is 'pur'.
'pur'+'r'='PURR'
'in' acts as a link.
(Other definitions for purr that I've seen before include "Express contentment" , "Cat's coo" , "Soft sound from car or cat" , "content? I might" , "Happy feline sound" .)