Horse betting attracts you first of all (3)
I believe the answer is:
bay
'horse' is the definition.
(bay is a kind of horse)
'betting attracts you first of all' is the wordplay.
'first of all' indicates taking the first letters.
The initial letters of 'betting attracts you' is 'BAY'.
(Other definitions for bay that I've seen before include "laurel maybe" , "Part of sea" , "Howl" , "Botany or Biscay, for example" , "Curved inlet; tree" .)