noun

puerility

pyoo-er-IL-uh-tee/ˌpjʊəˈrɪləti/

Childish immaturity in thought or behavior.

The puerility of their argument makes a serious discussion impossible.

A grown woman behaves childishly at a worktable, sticking out her tongue and making a fingers-in-ears taunting face toward a visibly unimpressed colleague.

Etymology

puerLatinchild, boy

+ilLatinof or relating to

+ityLatinstate or quality

The pieces describe the quality of being childlike or boyish. Latin puerilis already extended from youthfulness to trivial or silly behavior, supplying the negative sense of immaturity.

More examples

She has little patience for puerility in the workplace.
His prank reveals a surprising level of puerility.
The debate descends into puerility when the candidates trade insults.

Forms

puerility

puerile adjective — Showing childish immaturity or poor judgment.

Similar words

childishness: More commonly describes immature behavior inappropriate for someone's age.
immaturity: Covers a broader lack of emotional or intellectual development.
silliness: Often suggests harmless foolishness rather than a serious character flaw.