Quicker (6)
(Other definitions for sooner that I've seen before include "native of Oklahoma" , "At an earlier time" , "More readily; earlier" , "nickname of US State" , "Earlier than previously thought" .)
'quicker' is the definition.
(I know that quicker can be written as faster)
This is all the clue.
(Other definitions for faster that I've seen before include "with more security" , "Quicker" , "Strafe (anag)" , "More speedy" , "Lent Observer" .)