Enclosed by what pyramids must enclose (4)
I believe the answer is:
amid
'enclosed by' is the definition.
(I've seen this in another clue)
'what pyramids must enclose' is the wordplay.
'must enclose' indicates the answer is hidden within the clue.
'AMID' is hidden in the letters of 'what pyramids'.
(Other definitions for amid that I've seen before include "In the thick of" , "In the course of" , "Among" , "In the middle of" , "Maid (anag)" .)