deepyoudaoicibaDictYouDict[deep 词源字典]
deep: [OE] Deep is a member of a quite extensive and heterogeneous family of English words. It comes from a prehistoric Germanic *deupaz (source also of German tief, Dutch diep, and Swedish djup), which was a derivative of the base *d(e)u- ‘deep, hollow’. This may also have been the ancestor of the first syllable of dabchick ‘little grebe’ [16] (which would thus mean literally ‘diving duck’), while a nasalized version of it may underlie dimple. It produced dip, and a variant has given us dive.
=> dabchick, dimple, dip, dive[deep etymology, deep origin, 英语词源]
deep (adj.)youdaoicibaDictYouDict
Old English deop "profound, awful, mysterious; serious, solemn; deepness, depth," deope (adv.), from Proto-Germanic *deupaz (cognates: Old Saxon diop, Old Frisian diap, Dutch diep, Old High German tiof, German tief, Old Norse djupr, Danish dyb, Swedish djup, Gothic diups "deep"), from PIE *dheub- "deep, hollow" (cognates: Lithuanian dubus "deep, hollow, Old Church Slavonic duno "bottom, foundation," Welsh dwfn "deep," Old Irish domun "world," via sense development from "bottom" to "foundation" to "earth" to "world").

Figurative senses were in Old English; extended 16c. to color, sound. Deep pocket "wealth" is from 1951. 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).
deep (n.)youdaoicibaDictYouDict
Old English deop "deep water," especially the sea, from the source of deep (adj.).