Good to have garment (4)
I believe the answer is:
gown
'garment' is the definition.
(gown is a kind of garment)
'good to have' is the wordplay.
'good' becomes 'g' (abbreviation).
'to have' becomes 'own' ('own' can be a synonym of 'have').
'g'+'own'='GOWN'
(Other definitions for gown that I've seen before include "Long formal dress" , "Elegant dress" , "Loose flowing garment for woman or judge" , "Dress for formal occasions" , "Shift" .)