Entry 1 sense Webster, 1913 Childishness · Child·ish·ness · IPA /ˈt͡ʃaɪld.ɪʃ.nəs/ 01 n. The state or quality of being childish; simplicity; harmlessness; weakness of intellect. 1. The state or quality of being childish; simplicity; harmlessness; weakness of intellect.