A quay shelters a certain launch (7)
I believe the answer is:
pioneer
'launch' is the definition.
(I've seen this before)
'a quay shelters a certain' is the wordplay.
'a quay' becomes 'pier' (I've seen this in another clue).
'shelters' means one lot of letters goes inside another.
'a certain' becomes 'one' (ie one particular example of something).
'pier' enclosing 'one' is 'PIONEER'.
(Other definitions for pioneer that I've seen before include "To take first step" , "One who blazes the trail for others" , "One entering new territory" , "Trailblazer - initiate" , "Innovator; early settler" .)