Uncertainty of distinguishing feature in meaning (8)
I believe the answer is:
suspense
'uncertainty' is the definition.
(suspense is a kind of uncertainty)
'distinguishing feature in meaning' is the wordplay.
'distinguishing feature' becomes 'usp' (I am not sure about this - if you are sure you should believe this answer much more).
'in' is an insertion indicator.
'meaning' becomes 'sense' ('sense' can be a synonym of 'meaning').
'usp' put inside 'sense' is 'SUSPENSE'.
'of' acts as a link.
(Other definitions for suspense that I've seen before include "expectancy" , "Doubt" , "Discontinuance - indecision - excitement" , "Hitchcock's forte" , "Hitchcock's speciality" .)