n. 1
Deep intellect or insight.
Near-synonyms: brilliance, genius
n. 2
Depth; the state of possessing great downwards extent.
n. 3
The state of being profound; magnitude, gravity, or intensity.
The situation's profundity escaped most observers.

Forms

Plural: profundities → depths, deepnesses, wisdoms, astutenesses…

Choose the right word

Profundity, Insight, Judgment, Depth, Reason or Sagacity?

Insight, judgment, profundity or depth, reason, sagacity, sense, and understanding are native qualities of mind, tho capable of increase by cultivation.

J. C. Fernald, English Synonyms and Antonyms (1914)

Example sentences

depth Compared with his father, he is lacking in depth.
wisdom We admired his wisdom, not to mention his courage.
genius No one recognized Tom's genius while he was alive.
brilliance His brilliance has taken him quite some places in life.

Popularity over time

Word	1850 → 2019	Trend
profundity		steady
depth		falling
wisdom		rising
deepness		rising
astuteness		steady
genius		steady

Use in printed books, per decade from 1850 to 2019.

By length

5 letters: depth¹, abyss²
6 letters: wisdom², genius²
8 letters: deepness
10 letters: brilliance², astuteness³, abstrusity
12 letters: profoundness, abstruseness
13 letters: reconditeness

The small number after each word is its number of syllables (abyss² = 2 syllables).