dhewb-
“deep, hollow”deep, hollow, dig
Root for depth/hollowness, yielding English deep, dip, dive, Old English deop.
Discussion
The Proto-Indo-European root *dhewb- meant "deep, hollow." In Germanic, the root produced one of English's most elemental spatial words: deep (Old English dēop), along with depth and the related verbs dip and dive. German tief "deep" continues the same form with the High German consonant shift. Lithuanian dubùs "deep" and dùbti "to become hollow" confirm the Balto-Slavic reflexes. The semantic field is remarkably consistent: unlike roots that wander from concrete to abstract meanings, *dhewb- has remained anchored to the physical experience of vertical depth — the hollowed-out place, the sunken space, the measurement downward from surface to bottom. Rix does not list a verbal root *dhewb- in LIV², treating the attested forms as primarily denominal — the adjective "deep" came first, and verbs like dip and dive were derived from it. This nominal priority suggests that for the Proto-Indo-European speakers, depth was a named quality of the landscape before it became an action one could perform.
Notes
Pokorny 267-268. English deep, depth, dip, dive, dub.