Gold carriage in song, evergreen (9)
I believe the answer is:
araucaria
'evergreen' is the definition.
(I've seen this before)
'gold carriage in song' is the wordplay.
'gold' becomes 'Au' (Au is the chemical symbol for gold).
'carriage' becomes 'car' (eg a train car or train carriage).
'in' is an insertion indicator.
'song' becomes 'aria' (piece of music in an opera).
'au'+'car'='aucar'
'aucar' inserted within 'aria' is 'ARAUCARIA'.
(Other definitions for araucaria that I've seen before include "Monkey puzzle tree - Guardian cryptic crossword setter" , "Monkey puzzle tree (or Chile pine)" , "puzzle for primates?" , "Evergreen" , "Coniferous tree" .)