hollow

Hollow is an adjective meaning having an empty space inside, or not solid throughout. A hollow object has a cavity, shell, or interior void that distinguishes it from a solid mass. The term can describe both natural forms and manufactured items, and it is often used for parts designed to be lighter or to contain something else.

As a noun, a hollow is a natural depression in terrain, such as a low area between hills or a small valley that may host a stream. In parts of North America, it is common to hear hollow or holler for such a landscape feature, sometimes associated with a rural or mountainous area.

As a verb, to hollow means to remove material from the inside of an object to create a cavity or hollow space. Examples include hollowing out a log, a coconut, or a sculpture. Hollowing can reduce weight, create a container, or alter acoustic properties.

In biology and medicine, hollow can describe organs or structures that contain a lumen, such as the stomach or blood vessels. Birds have hollow bones, a feature that reduces weight. In engineering, hollow cores and shells are common in construction, materials science, and product design to achieve strength with less material.

In culture and language, hollow is used metaphorically to indicate something that lacks real substance or sincerity, as in hollow promises or hollow invocations. The term is also used in acoustics and instrument design to describe a resonant yet recessed quality in sound.