1. (noun) a bicycle with two sets of pedals and two seats

• bicycle-built-for-two
• tandem bicycle

2. (adverb) one behind the other

• in tandem

1. (noun) an arrangement of two or more objects or persons one behind another

• arrangement
• placement

2. (noun) a bicycle with two sets of pedals and two seats

• bicycle
• bike
• cycle
• wheel