Also bet on, but it’s slow (7)
I believe the answer is:
andante
'it's slow' is the definition.
('andante' can be similar in meaning to 'slow')
'also bet on' is the wordplay.
'also' becomes 'and' (I've seen this before).
'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" .)