Vigorously, deviously or subtly (8)
I believe the answer is:
robustly
'vigorously' is the definition.
(thesaurus)
'deviously or subtly' is the wordplay.
'deviously' indicates anagramming the letters (I've seen this in other clues).
'or'+'subtly'='orsubtly'
'orsubtly' is an anagram of 'ROBUSTLY'.
(Other definitions for robustly that I've seen before include "In strong, vigorous manner" , "In a sturdy and healthy manner" , "In a vigorous way" .)