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puerile (pu·er·ile): / PYOOR il | PYOO er il /
adjective

(1) childishly silly or foolish; trivial or immature
(2) relating to childhood; juvenile

[Possibly from or via French puéril, or directly from Latin puerilis meaning “boyish,” from Latin puer meaning “boy.”]

Usage: I asked for your best literary effort, yet the paper you submitted represented puerile writing at best.