Swimmer clipped part of motor (5)
I believe the answer is:
turbo
'motor' is the definition.
(I've seen this before)
'swimmer clipped' is the wordplay.
'swimmer' becomes 'turbot' (type of fish).
'clipped' means to remove the last letter (the word is shortened or clipped).
'turbot' with its last letter removed is 'TURBO'.
'part of' is the link.
(Other definitions for turbo that I've seen before include "motor" , "Charger improves a car's power" , "source of power" , "Powerful device" , "Gastropod" .)