Maintain some mythological legends (6)
I believe the answer is:
allege
'maintain' is the definition.
(I know that allege is a more specific form of the action maintain)
'some mythological legends' is the wordplay.
'some' indicates a hidden word (some of the parts of the word are used).
'ALLEGE' can be found hidden inside 'mythological legends'.
(Other definitions for allege that I've seen before include "Declare or assert without proof" , "Declare without absolute proof" , "Aver - maintain" , "Aver (without proof)" , "hold" .)