Petition involving son shuts up apprehension (8)
I believe the answer is:
suspense
'apprehension' is the definition.
(I know that suspense is a type of apprehension)
'petition involving son shuts up' is the wordplay.
'petition' becomes 'sue' (both can mean to appeal or ask for something).
'involving' means one lot of letters goes inside another.
'son' becomes 's' (genealogical abbreviation for son).
'shuts up' becomes 'pens' (I can't explain this - if you can you should believe this answer much more).
's'+'pens'='spens'
'sue' going around 'spens' is 'SUSPENSE'.
Can you help me to learn more?
(Other definitions for suspense that I've seen before include "State of apprehension about what's going to happen" , "Apprehension, anticipation" , "expectancy" , "Doubt" , "The 3 of having to wait" .)