Also bet on, but it's slow (7)
I believe the answer is:
andante
'it's slow' is the definition.
(similar in meaning)
'also bet on' is the wordplay.
'also' becomes 'and' (both can mean in addition).
'bet on' becomes 'ante' (anteing is a kind of betting on).
'and'+'ante'='ANDANTE'
'but' acts as a link.
(Other definitions for andante that I've seen before include "at a gentle pace" , "Moving fairly slowly" , "moving steadily" , "Fairly slow (mus.)" , "Moderately slow movement" .)