Other forms: depths
Depth is how far something goes down from the surface. The depth of the water, a depth of two metres, measure the depth.
It also means the far inner part of something: the depths of the ocean, the depths of winter, the depths of despair. Figuratively, depth means seriousness and substance — depth of feeling, a book with real depth, out of my depth. In depth means thorough: an in-depth study. Note out of your depth, meaning both literally too deep to stand and figuratively beyond your ability.
1noundepthHow far something goes down from the surface.
“The pool's depth is marked on the tiles at each end.”
2nounseriousnessSeriousness or substance.
“The argument has no depth once you push at it.”
Too few real examples of this word to estimate which sense is commonest.
depth is a measure downward, or substance.
Depth is deep plus -th, the same ending that makes length from long, breadth from broad and strength from strong. It is one of English's oldest ways of turning an adjective into a measurement.
Proto-Indo-European
*dʰewbʰ-
Proto-Germanic
*diupiþō — depth
Old English
*dīepþ — depth
Middle English
depthe
English, today
depth
From Middle English depthe, from Old English dīepþ (“depth”), from Proto-Germanic diupiþō (“depth”), equivalent to deep + th. 2 Cognate with Scots deepth, stq Djüpte, West Frisian djipte (“depth; abyss, chasm”), Dutch diepte, German Low German Deepd, lb Déift, Danish -, Norwegian Bokmål dybde (“depth”), Faroese dýpd (“depth”), Icelandic dýpt, Norwegian Nynorsk djupt, dypt, and Gothic 𐌳𐌹𐌿𐍀𐌹𐌸𐌰 (“depth”); further to Old English diepe, German Tiefe, Icelandic dýpi, Norwegian Nynorsk djup, djupn, Swedish djup.
Etymology from Wiktionary, CC BY-SA