'clownishness' originates from English, specifically from the adjective 'clownish' (formed from the noun 'clown' + the suffix '-ish') with the additional noun-forming suffix '-ness' to denote a state or quality.

'clown' appeared in Middle English as 'clowne' meaning a rustic or boorish person; it possibly relates to dialectal terms and may be influenced by Old Norse dialectal forms such as 'klunni' (a clumsy fellow). The adjective 'clownish' developed by adding '-ish' to 'clown', and later '-ness' was attached to produce 'clownishness'.

Initially, 'clown' referred to a rustic, clumsy, or boorish person; over time it came to denote a comic performer or buffoon, and 'clownishness' now denotes the quality of being clown-like or foolish.