Incredibly fast side I found to be contented (9)
I believe the answer is:
satisfied
'to be contented' is the definition.
(similar in meaning)
'incredibly fast side i' is the wordplay.
'incredibly' is an anagram indicator.
'fast'+'side'+'i'='fastsidei'
'fastsidei' with letters rearranged gives 'SATISFIED'.
'found' acts as a link.
(Other definitions for satisfied that I've seen before include "relieved of doubt" , "as one may be with a second helping" , "served" , "given answer > was convincing" , "Content" .)