Famous old Hollywood actress, good in the last act (8)
I believe the answer is:
swansong
'the last act' is the definition.
(I've seen this before)
'famous old hollywood actress good' is the wordplay.
'famous old hollywood actress' becomes 'swanson' (silent film star Gloria Swanson).
'good' becomes 'g' (abbreviation).
'swanson'+'g'='SWANSONG'
'in' acts as a link.
(Other definitions for swansong that I've seen before include "Last act" , "Final work or performance" , "last performance" , "Final appearance" , "Last call" .)