1
a tandem
tandem 用作可数名词，指“串座双人自行车”，是 a tandem bicycle 的省略说法。
We rented a tandem and rode along the river.
我们租了一辆双人自行车，沿着河骑行。
纵列；一前一后的排列；串座双人自行车
tandems — plural of tandem
先理解核心含义，再看它在真实句子里的用法。
纵列；一前一后的排列；串座双人自行车
an arrangement of two or more objects or persons one behind another; a bicycle for two riders one behind the other
We rented a tandem and rode along the river.
我们租了一辆双人自行车，沿着河骑行。
由两匹以上前后串联的挽畜(通常为挽马)拉的车,前面的挽畜负责转向。
A carriage pulled by two or more draught animals (generally draught horses) harnessed one behind the other, both providing pulling power but only the animal in front being able to steer.
两个或多个物体或人一前一后的排列
an arrangement of two or more objects or persons one behind another
两匹前后串联套在一起的挽畜(通常为挽马)。
Two draught animals (generally draught horses) harnessed one behind the other.
双人自行车
a bicycle with two sets of pedals and two seats
We rented a tandem for the afternoon and rode along the river.
我们下午租了一辆双人自行车，沿着河骑行。
My sister and I bought a tandem last spring, so we can enjoy cycling together.
我和姐姐去年春天买了一辆双人自行车，这样我们就可以一起享受骑行的乐趣。
Riding a tandem takes practice because both riders need to pedal in sync.
骑双人自行车需要练习，因为两位骑车人需要同步踩踏板。
tandem 用作可数名词，指“串座双人自行车”，是 a tandem bicycle 的省略说法。
We rented a tandem and rode along the river.
我们租了一辆双人自行车，沿着河骑行。
tandem 作形容词，放在名词前，表示“一前一后的；纵排的”。
The apartment building offers tandem parking.
这栋公寓楼提供纵列式停车位。
in tandem 是固定介词短语，常用作状语，表示“一前一后地”。
The two horses were harnessed in tandem.
这两匹马被一前一后地套上挽具。
Not this
They worked tandem on the project.
Use this
They worked in tandem on the project.
“tandem” 作“协同地”讲时，必须用固定短语 “in tandem”，不能省略介词 in。tandem 单独作副词意为“一前一后地”，与“协同”无关，因此原句语义不明；加上 in 后才表达“协同”。
Not this
She collaborated with her team in tandem to the plan.
Use this
She collaborated with her team in tandem with the plan.
“in tandem with” 是固定搭配，表示“与……协同”，介词必须用 with，不能用 to。用 to 是受“与……一致”或 in relation to 等表达干扰产生的错误。
Focus on the distinctions below. Other candidates are kept compact until a reliable usage note is available.
与…同时；与…协同
The new policy was introduced in tandem with a public awareness campaign.
新政策与公众宣传活动同时推出。
双人自行车（两人一前一后骑行）
They bought a tandem bicycle for their weekend rides.
他们买了一辆双人自行车，用于周末骑行。
双人跳伞（学员与教练连在一起跳伞）
For her birthday, she tried tandem skydiving.
为了庆祝生日，她体验了双人跳伞。
协同地；同时进行地
The two departments worked in tandem to finish the project.
两个部门协同工作以完成这个项目。
与…合作；配合…
Doctors and nurses act in tandem with each other in emergencies.
在紧急情况下，医生和护士相互配合。
Use tandems naturally, then get feedback on meaning, tone, grammar, and phrasing.
Revisit a common error or keep this word in your review list.
想象tandem双人自行车：两个座位一前一后，车就是纵排排列，记住'tandem=一前一后'。
语域：mixed 常见场景：bicycle riding、technical or academic writing、business or everyday collaboration tandem 的正式程度通常随搭配和语境变化：日常提到双人自行车时多说 tandem bike，语气比较随意；在技术或学术表述中（如 tandem axle、in tandem）则比较正式。整体语域标为 mixed，建议根据具体搭配选择。
名词复数形式为 tandems。
Dictionary facts from ECDICT, WIKTIONARY.