The inner sole of a shoe. Compare 中敷 (なかじき), which is a removable insert placed on top of the insole.
See also: 中敷き (なかじき)
この靴は中底が柔らかくて歩きやすい。
These shoes have soft insoles and are easy to walk in.
perforated divider in a food steamer
A flat, perforated tray or divider placed inside a steamer to separate food from the water below. Often used in cooking contexts.
蒸し器の中底にクッキングシートを敷いて、肉まんを並べる。
Line the steamer's perforated divider with parchment paper and arrange the meat buns.
Compound of 中 (なか, 'inside') and 底 (そこ, 'bottom'), with rendaku voicing of そこ to ぞこ. The meaning 'insole' is literal; the steamer sense is an extended use referring to the inner bottom tray of a steamer.