Some within round pillbox (4)
I believe the answer is:
inro
'pillbox' is the definition.
(I've seen this before)
'some within round' is the wordplay.
'some' indicates the answer is hidden within the clue (some of the parts of the word are used).
'INRO' is hidden within 'within round'.
(Other definitions for inro that I've seen before include "Small box for medicines" , "small container" , "Japanese box" , "ornamental chest" , "Underground level" .)