American for a time sure to miss small opening (8)
I believe the answer is:
aperture
'opening' is the definition.
(I know that aperture is a type of hole)
'american for a time sure to miss small' is the wordplay.
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'for a' becomes 'per' ('per' can mean 'for each' person or 'for a' person).
'time' becomes 't' (abbreviation).
'to miss' is a deletion indicator.
'small' becomes 's' (abbreviation - e.g. clothes size).
'sure' with 's' taken away is 'ure'.
'a'+'per'+'t'+'ure'='APERTURE'
(Other definitions for aperture that I've seen before include "Opening through which light enters a camera" , "Opening, mostly small" , "Small hole or opening" , "Opening (for a photographer?)" , "Device controlling amount of light admitted" .)