Gotten too big for unfashionable dress? Finally, tailor gets brought in (8)
I believe the answer is:
outgrown
'gotten too big for' is the definition.
(I've seen this in another clue)
'unfashionable dress? finally tailor gets brought in' is the wordplay.
'unfashionable' becomes 'out' (synonyms).
'dress?' becomes 'gown' (gowning is a kind of dressing).
'finally' suggests the final letters.
'gets brought in' is an insertion indicator.
The final letter of 'tailor' is 'r'.
'gown' enclosing 'r' is 'grown'.
'out'+'grown'='OUTGROWN'
(Another definition for outgrown that I've seen is " Too big or mature for".)