Pet project, great instrument (4,5)

I believe the answer is:

baby grand

'instrument' is the definition.
(baby grand is a kind of instrument)

'pet project great' is the wordplay.
'pet project' becomes 'baby' (I've seen this before).
'great' becomes 'grand' (I've seen this before).
'baby'+'grand'='BABY GRAND'

(Other definitions for baby grand that I've seen before include "Type of piano" , "Instrument" , "Small, non-upright piano" , "Infant piano?" , "Smaller piano" .)

I've seen this clue in the Sydney Morning Herald.

Want a hint initially instead of a full solution? Install my app