Tandem

adverb
1.
one following or behind the other:
to drive horses tandem.
adjective
2.
having animals, seats, parts, etc., arranged tandem or one behind another.
noun
3.
a vehicle, as a truck, tractor, or trailer, in which a pair or pairs of axles are arranged in tandem.
4.
tandem bicycle.
5.
tandem trailer (def 1).
6.
a team of horses harnessed one behind the other.
7.
a two-wheeled carriage with a high driver’s seat, drawn by two or more horses so harnessed.
8.
any of various mechanisms having a tandem arrangement.
Idioms
9.
in tandem,

in single file:
They swam in tandem.
in association or partnership.

noun
1.
a bicycle with two sets of pedals and two saddles, arranged one behind the other for two riders
2.
a two-wheeled carriage drawn by two horses harnessed one behind the other
3.
a team of two horses so harnessed
4.
any arrangement of two things in which one is placed behind the other
5.
in tandem, together or in conjunction
adjective
6.
(Brit) used as, used in, or routed through an intermediate automatic telephone exchange: a tandem exchange
adverb
7.
one behind the other: to ride tandem