Perhaps an atom quietly splits? (7)
I believe the answer is:
article
'perhaps an' is the definition.
('an' is an indefinite article in English)
'atom quietly splits?' is the wordplay.
'atom' becomes 'particle' (both can mean a small amount of something).
'quietly' becomes 'p' (p for piano and quiet).
'splits?' indicates named letters should be taken away.
'particle' with 'p' taken away is 'ARTICLE'.
(Other definitions for article that I've seen before include "For instance, a" , "Perhaps an" , "Thing - composition - item" , "Piece of journalism" , "to cause amusement, say, to a king" .)