As practice, start to execute dance (9)
I believe the answer is:
quadrille
'dance' is the definition.
(quadrille is a kind of dance)
'as practice start to execute' is the wordplay.
'as' becomes 'qua' ('qua' is a Latin term meaning 'in the capacity of').
'practice' becomes 'drill' (synonyms).
'start to' indicates taking the first letters.
The first letter of 'execute' is 'e'.
'qua'+'drill'+'e'='QUADRILLE'
(Other definitions for quadrille that I've seen before include "Old square dance (performed by lobsters in Alice in Wonderland)" , "(Music for a) square dance for four or more couples" .)