Stuff about even pieces of antique skull (7)
I believe the answer is:
cranium
'skull' is the definition.
(I've seen this in another clue)
'stuff about even pieces of antique' is the wordplay.
'stuff' becomes 'cram' (synonyms).
'about' indicates putting letters inside.
'even pieces of' indicates alternate letters (letters in even-numbered positions).
The alternating letters of 'antique' are 'niu'.
'cram' enclosing 'niu' is 'CRANIUM'.
(Other definitions for cranium that I've seen before include "Brain container" , "The skull, major head bone" , "Brainbox" , "hard case" , "Part of the skull" .)