Dance as mainly trained (9)
I believe the answer is:
quadrille
'dance' is the definition.
(quadrille is a kind of dance)
'as mainly trained' is the wordplay.
'as' becomes 'qua' (I've seen this before).
'mainly' means to remove the last letter.
'trained' becomes 'drilled' (drilling is a kind of training).
'drilled' with its final letter removed is 'drille'.
'qua'+'drille'='QUADRILLE'
(Other definitions for quadrille that I've seen before include "(Music for a) square dance for four or more couples" , "Old square dance (performed by lobsters in Alice in Wonderland)" .)