Fie! I intend to be devious and vague (10)
I believe the answer is:
indefinite
'vague' is the definition.
(I've seen this before)
'fie i intend to be devious' is the wordplay.
'to be devious' indicates an anagram.
'fie'+'i'+'intend'='fieiintend'
'fieiintend' is an anagram of 'INDEFINITE'.
'and' acts as a link.
(Other definitions for indefinite that I've seen before include "Like a" , "Not certain" , "Vague" , "Unsettled" , "rough" .)