Swift, rapid (5)
I believe the answer is:
fleet
I believe this is a double definition.
'swift' is the first definition.
(synonyms)
'rapid' is the second definition.
(I've seen this before)
(Other definitions for fleet that I've seen before include "Fast - naval force" , "cars en masse?" , "Fast; London street, old prison" , "Swift; armada" , "fast is observed" .)