double bottom; false bottom; double sole; double hull
Refers to a second, often hidden, bottom layer in containers, ships, shoes, etc. Used in contexts like smuggling, insulation, or reinforcement.
The trunk had a false bottom where contraband was hidden.
This ship has a double-bottom structure, making it very safe.
Compound of 二重 (nijū, 'double') and 底 (soko, 'bottom'). The reading ぞこ is a rendaku form of そこ.