O.E. deop, from P.Gmc. *deupaz, from PIE *d(e)u- "deep, hollow" (cf. O.C.S. duno "bottom, foundation," O.Ir. domun "world," via sense development from "bottom" to "foundation" to "earth" to "world"). Figurative sense was in O.E.; extended 16c. to color, sound. Deep pocket "wealth" is from 1951. Deep-freeze was a registered trademark (U.S. Patent Office, 1941) of a type of refrigerator; used generically for "cold storage" since 1949. To go off the deep end "lose control of oneself" is slang first recorded 1921, probably in reference to the deep end of a swimming pool, where a person on the surface can no longer touch bottom. When 3-D films seemed destined to be the next wave and the biggest thing to hit cinema since "talkies," they were known as deepies (1953). The gods have spared us.
O.E. deoplice (see deep), used in both literal and figurative senses.
The Dictionary of American Slang, Fourth Edition by Barbara Ann Kipfer, PhD. and Robert L. Chapman, Ph.D. Copyright (C) 2007 by HarperCollins Publishers. Cite This Source
deeper in the Bible
used to denote (1) the grave or the abyss (Rom. 10:7; Luke 8:31); (2) the deepest part of the sea (Ps. 69:15); (3) the chaos mentioned in Gen. 1:2; (4) the bottomless pit, hell (Rev. 9:1, 2; 11:7; 20:13).