Plimsolls (5)
I believe the answer is:
pumps
'plimsolls' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for pumps that I've seen before include "Forces liquid to move; light shoes" , "footwear" , "Mechanical devices that move fluid or gas" , "needed by cyclists" , "Cycle attachments" .)