What does depth mean?
Depth refers primarily to the downward or inward distance from a surface to its furthest point — the depth of a lake, a trench, or a shelf. Beyond physical measurement, the word carries rich figurative weight: it describes intensity of emotion ('the depth of her grief'), profundity of thought ('a philosopher of great depth'), and thoroughness of analysis or knowledge ('the report examines the issue in depth'). Derived from the Old English adjective 'deop' (deep), it belongs to a small family of English abstract nouns formed from adjectives, alongside 'length', 'strength', and 'width'. Its connotations are generally positive when describing intellect and character — suggesting substance, seriousness, and complexity — though phrases like 'the depths of despair' show it can also mark the lowest or darkest points of experience. Whether measuring oceans or minds, depth signals that there is more beneath the surface than first meets the eye.
The distance from the top or surface of something to its bottom; the state or degree of being deep.
"The pool has a maximum depth of two metres."
Often used with prepositions like 'to' and 'at': 'to a depth of', 'at a depth of'.
Intensity, profundity, or thoroughness of emotion, thought, knowledge, or treatment.
"The course covers the subject in considerable depth."
(Usually plural: depths) A deep or remote place, especially the deepest part of the sea, or the most extreme degree of something.
"The shipwreck lay forgotten in the ocean's depths."
The plural 'depths' is typically used for deep places (especially of water), extreme degrees ('the depths of despair'), or multiple measurements. The singular is preferred for literal measurements.
"The submarine explored the uncharted depths of the Pacific."
English borrowed 'depth' from 'deep' by analogy with pairs like 'long/length' and 'strong/strength' — but unlike those, it kept the vowel of its root word.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of depth
Depth derives from Middle English 'depthe', formed from the Old English adjective 'deop' (deep) combined with the suffix '-th(e)', which turns adjectives into abstract nouns — the same pattern seen in 'long' → 'length' and 'strong' → 'strength'. Interestingly, while most words in this pattern underwent vowel changes, 'depth' largely retained the vowel of its root adjective, making it somewhat irregular among its siblings. It is cognate with related Germanic forms such as Old Norse 'djúp'.
Related word forms
How depth is actually used
'Depth' is neutral in register and works in both formal and everyday contexts. The phrase 'in depth' (as in 'an in-depth analysis') is extremely common in journalism and academic writing. In its plural form 'the depths', the word often carries a slightly literary or dramatic tone, as in 'the depths of winter'.
Easily confused with depth
Breadth measures width from side to side, while depth measures how far down or in something extends; both also differ figuratively (broad knowledge vs. profound insight).