库 kù armory
armory; treasury; warehouse
How it came to be
A cart standing under a lean-to roof. War chariots were the most valuable thing a state owned and they were kept under cover: the shed with the cart in it is the store.
How it is used
- 库 is a bound noun for a storage place - warehouse, depot, reservoir - always attached to what's stored: 车库 (chēkù) garage, 仓库 (cāngkù) warehouse, 水库 (shuǐkù) reservoir.
- 数据库 (shùjùkù) "database" is the standard tech-loanword pattern, mirroring how English builds compound nouns.
- 库存 (kùcún) is a business term for inventory/stock on hand, e.g. 库存不足 (kùcún bùzú) out of stock.
- Never used alone to mean "a store/warehouse" in casual speech - you'd need one of these compounds.