1. A description of igneous rocks, especially in the form of dikes or sills, created when molten magma rose to the surface of the earth's crust but solidified before reaching it: The hypabyssal layer of rock was an impediment to the oil drilling in the ocean.
2. Designating a rock in texture that is intermediate between plutonites (a deep-seated rock) and extrusive rocks (forced out at the surface) which are usually formed at moderate distances below the surface: The term hypabyssal is part of the vocabulary used in the science of petrology.

The survey of the ocean floor indicated an extensive layer of hypabyssal hard consolidated mineral matter on the bottom.