Tension -- feeling keeping us quiet (8)
I believe the answer is:
suspense
'tension' is the definition.
(suspense can mean tension or uncertainty)
'feeling keeping us quiet' is the wordplay.
'feeling' becomes 'sense' (feeling can mean a sensation).
'keeping' indicates putting letters inside (some letters kept inside).
'quiet' becomes 'p' (music symbol for 'piano', ie soft or quiet).
'us'+'p'='usp'
'sense' going around 'usp' is 'SUSPENSE'.
(Other definitions for suspense that I've seen before include "State of anxious excitement" , "expectancy" , "State of anxious uncertainty while waiting (8)" , "State of anxiety while waiting" , "Excited anticipation of approaching climax" .)