immaturityEnglishOxford American Thesaurusimmaturity noun 1 the immaturity of the fruit | the immaturity of the technology: unripeness, greenness, sourness; newness, rawness, crudeness, crudity, imperfection, incompleteness, lack of completion, lack of development. 2 they were shocked by such immaturity in a grown man: childishness, babyishness, infantilism, juvenility, puerility, lack of experience, inexperience, unworldliness, naivety, ingenuousness.