Good musical instrument to take up for free (6)
I believe the answer is:
gratis
'free' is the definition.
(I know that free can be written as gratis)
'good musical instrument to take up' is the wordplay.
'good' becomes 'g' (abbreviation).
'musical instrument' becomes 'sitar' (sitar is a kind of musical instrument).
'to take up' shows that the letters should be reversed in order (I've seen 'taken up' mean this).
'sitar' reversed gives 'ratis'.
'g'+'ratis'='GRATIS'
'for' acts as a link.
(Other definitions for gratis that I've seen before include "Without payment" , "not charged" , "On the house" , "Free, at no cost" , "Free of charge" .)