垫底儿
垫底 (墊底) diàn​dǐ
foundation verb
to lay a foundation or a base for future development

这些基础课程是为以后的专业学习垫底。

zhè​xiē jī​chǔ kè​chéng shì wèi yǐ​hòu de zhuān​yè xué​xí diàn​dǐ.

These basic courses lay the foundation for future specialized studies.

rank last verb
to be at the very bottom of a ranking or competition

他在这次模拟考试中成绩不幸垫底。

tā zài zhè cì mó​nǐ kǎo​shì zhōng chéng​jì bù​xìng diàn​dǐ.

Unfortunately, he finished last in this mock exam.

tide over verb
to eat a small amount of food to prevent hunger before a main meal

离晚饭还有两小时，你先吃个包子垫底。

lí wǎn​fàn hái yǒu liǎng xiǎo​shí, nǐ xiān chī gè bāo​zi diàn​dǐ.

Dinner is still two hours away; have a steamed bun first to tide you over.

underlay verb
to put something on the bottom or underneath for protection or support

他在箱子下面铺了几层厚纸来垫底。

tā zài xiāng​zi xià​miàn pū le jǐ céng hòu zhǐ lái diàn​dǐ.

He lined the bottom of the box with several layers of thick paper.