Maintains as taking in resolve (5)
I believe the answer is:
avows
'maintains' is the definition.
(I've seen this in another clue)
'as taking in resolve' is the wordplay.
'taking in' means one lot of letters goes inside another.
'resolve' becomes 'vow' (I've seen this in another clue).
'as' going around 'vow' is 'AVOWS'.
(Other definitions for avows that I've seen before include "Swears" , "Affirms as true" , "Declares solemnly" .)