noun

1. a long, narrow, open container of wood, stone, etc. for holding water or food for animals
2. any similarly shaped vessel, as one for kneading or washing something
3. a channel or gutter, esp. one under the eaves of a building, for carrying off rainwater
4. a long, narrow hollow or depression, as between waves
5. a low in any cycle, esp. in an economic cycle
6. a long, narrow area of low barometric pressure

Etymology: ME < OE trog, akin to Ger < IE *druk- < base *deru-, tree: basic sense, “hollowed wooden object”