墊底〔垫-〕 zin³ dai² {diàn dǐ}

deductible (insurance term); people who are at the bottom, especially students who have poor academic performance; to put something at the bottom

墊底兒〔垫-儿〕 din⁶ dai² ji⁴ {diàn dǐ r}

1. foundation layer
2. underlay
3. fig. to lay foundations
4. to snack