Fast run with a tight finish (5)
I believe the answer is:
fleet
'fast' is the definition.
(similar in meaning)
'run with a tight finish' is the wordplay.
'run' becomes 'flee' (I've seen this in other clues).
'with' means one lot of letters go next to another.
'finish' says to take the final letters.
The final letter of 'tight' is 't'.
'flee'+'t'='FLEET'
(Other definitions for fleet that I've seen before include "flying?" , "Group of aircraft, ships or cars" , "bowler famously intercepted one once" , "Swift like naval force" , "good turn of speed" .)