In unrestrained revels I will be submissive (7)
I believe the answer is:
servile
'submissive' is the definition.
(similar in meaning)
'in unrestrained revels i' is the wordplay.
'in' is an insertion indicator.
'unrestrained' indicates an anagram.
'revels' with letters rearranged gives 'servle'.
'servle' enclosing 'i' is 'SERVILE'.
'will be' acts as a link.
(Other definitions for servile that I've seen before include "Cringing, fawning" , "Fawning; menial" , "Toadying" , "grovelling" , "Sycophantic" .)