one following or behind the other

to drive horses tandem.

having animals, seats, parts, etc., arranged tandem or one behind another.

a vehicle, as a truck, tractor, or trailer, in which a pair or pairs of axles are arranged in tandem.

tandem bicycle.

tandem trailer ( def. 1 ) .

a team of horses harnessed one behind the other.

a two-wheeled carriage with a high driver's seat, drawn by two or more horses so harnessed.

any of various mechanisms having a tandem arrangement. ?

in tandem

in single file

They swam in tandem.

in association or partnership.