Round part of a razor blade (3)
I believe the answer is:
orb
'round' is the definition.
(thesaurus)
'part of a razor blade' is the wordplay.
'part of' indicates a hidden word.
'ORB' is hidden in the letters of 'razor blade'.
(Other definitions for orb that I've seen before include "The World" , "Heavenly body" , "Spherical object or shape" , "Ceremonial globe carried by a monarch" , "Spherical symbol of monarch's power" .)