Secure the rope to the jetty, it's swifter (7)
I believe the answer is:
nippier
'swifter' is the definition.
Both the definition and answer are comparative adjectives. Perhaps they are linked in a way I don't understand?
'secure the rope to the jetty' is the wordplay.
'secure the rope' becomes 'nip' (I can't explain this - if you can you should believe this answer much more).
'to the jetty' becomes 'pier' (I've seen this before).
'nip'+'pier'='NIPPIER'
'it's' acts as a link.
Can you help me to learn more?
(Other definitions for nippier that I've seen before include "More sprightly" , "More frosty" , "more active" .)