An Etymological Dictionary of Astronomy and Astrophysics

1. A Hydroxyl radical formed by abstraction of a hydrogen atom from water.
   
2. An OH group within a molecule.

See also: From → hydro- + ox(y)- a combining form meaning “sharp, acute, pointed, acid,” used in the formation of compound words, from Gk, oxys “sharp, keen, acid” + -yl a suffix used in the names of chemical radicals, from Fr. -yle, from Gk. hyle “matter, substance.”