Narrow notch (4)
I believe the answer is:
slot
'narrow notch' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for slot that I've seen before include "Lots (anag.)" , "Space for coin or programme" , "Scheduled time - hierarchical position" , "Scheduled time -- aperture for coins" , "Narrow opening, for cash say" .)