Greek character in Bow turned up skull (7)
I believe the answer is:
cranium
'skull' is the definition.
(I've seen this in another clue)
'greek character in bow turned up' is the wordplay.
'greek character' becomes 'mu' (letter of the Greek alphabet).
'bow' becomes 'arc' (both can mean a curve).
'turned up' is a reversal indicator.
'mu'+'in'+'arc'='muinarc'
'muinarc' backwards is 'CRANIUM'.
(Other definitions for cranium that I've seen before include "Part of the skull" , "Skull that encloses the brain" , "Braincase" , "Skull of a vertebrate" , "The skull, bone enclosing brain" .)