Arms whirling on dancer (8)
I believe the answer is:
ordnance
'arms' is the definition.
(ordnance is a kind of arms)
'whirling on dancer' is the wordplay.
'whirling' indicates anagramming the letters.
'on'+'dancer'='ondancer'
'ondancer' is an anagram of 'ORDNANCE'.
(Other definitions for ordnance that I've seen before include "Military supplies and materials" , "Survey may follow this" , "guns etc." , "weapons" , "Car on end (anag) - artillery" .)