Bicycle for two (6)
I believe the answer is:
tandem
'bicycle for two' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for tandem that I've seen before include "Bike with two saddles" , "Two-seater bike" , "Two-person bike" , "Two-seater bicycle" , "One behind another, as on bicycle" .)