Abstract: A drinking vessel configured for a removable engagement with the capped end of a bottle through engagement with the bottle or the cap. The device features a fluid cavity separated from a base cavity by a central wall, which is configured for drinking or pouring a measured amount of liquid therefrom. The device is engageable to the bottle or cap by insertion of the cap end of the bottle, into a cavity in the base end, and exerting force along an axial line running through the bottle. A frictional engagement between surfaces of the device and the bottle is achieved which may be enhanced by biasing components.