1 adj Something or someone that is immature is not yet completely grown or fully developed.
She is emotionally immature.
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immaturity n-uncount
In spite of some immaturity in the figure drawing and painting, it showed real imagination.
2 adj If you describe someone as immature, you are being critical of them because they do not behave in a sensible or responsible way., (disapproval)
She's just being childish and immature.
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immaturity n-uncount
...his immaturity and lack of social skills.