Bed on wheels (3)
(Other definitions for cot that I've seen before include "Function" , "Baby's bed" , "Crib" , "Baby bed" , "Folding bed - fingerstall" .)
'bed on wheels' is the definition.
(I've seen this in another clue)
This is all the clue.
(Another definition for rollaway that I've seen is " American bed with castors".)