Old actress grand in last hurrah (8)
(Other definitions for swansong that I've seen before include "Last call" , "Last act" , "Final appearance" , "Final work or performance" , "last performance" .)
'last hurrah' is the definition.
(I know that last hurrah can be written as swan song)
'old actress grand' is the wordplay.
'old actress' becomes 'swanson' (I've seen this before).
'grand' becomes 'g' (G is short for grand as in a thousand).
'swanson'+'g'='SWAN-SONG'
'in' acts as a link.
(Other definitions for swan song that I've seen before include "Last appearance" , "Final utterance" , "Final performance, to the tune of an aquatic bird" , "A dying performance" , "Last performance of a career" .)