/hip'euh bis"euhl, huy'peuh-/ , adj. Geol.
1. (of an igneous rock) intermediate in texture between coarse-grained intrusive rocks and fine-grained extrusive rocks.
2. noting any of various minor intrusions, as dikes and sills, that have crystallized under conditions intermediate between plutonic and extrusive.
[ 1890-95; HYP- + ABYSSAL ]