(sports) A rule regarding play on a specific field, course, or court. / (idiomatic, usually in the plural) The basic rules or standards; whatever someone must know before proceeding.

A thick copper bar required in telecommunication room installations to provide a central ground-point for equipment.

(aeronautics) Any aerodynamic effects occurring due to a vehicle's body or appendages moving in close proximity to the ground.

A place or region where animals go to breed. / (figuratively) A place or institution seen as creating large numbers of a stated thing, type of person, etc.

(intransitive, especially of an animal, chiefly UK) To escape into a burrow, hole, etc. when being hunted.

Of a person: having extensive knowledge of a subject. / Of an argument, etc.: based on good judgment and solid reasoning.

Alternative form of groundwater

Any member of the order Carcharhiniformes, the largest order of sharks with over 270 species. / A Greenland shark, Somniosus microcephalus.

(physics) The stationary state of lowest energy of a particle or system of particles.

(idiomatic) The situation in reality as opposed to in the abstract. / (literally) Some aspects of the situation in a particular location.