childish

If you act immature or bratty, you're being childish. A childish dinner guest might pout because you didn't make dessert.

While the adjective childish is sometimes used to simply mean "like a child," it's more common to use childlike in this way. When your teacher comments that your chattering during class is childish behavior, she means that you're acting as juvenile as a four year old child. This negative implication has been attached to childish since the 15th century. The word comes from the Old English cildisc, "proper to a child."

Definitions of childish
  1. adjective
    indicating a lack of maturity
    childish tantrums”
    synonyms: infantile
    immature
    characteristic of a lack of maturity
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