1. (n.) An idiom; a form, mode of expression, or signification, peculiar to a language.

2. (n.) Lack of knowledge or mental capacity; idiocy; foolishness.

arrested development backwardness blithering idiocy cretinism half-wittedness idiocy idiotism imbecility infantilism insanity mental defectiveness mental deficiency mental handicap mental retardation mongolianism mongolism mongoloid idiocy moronism moronity profound idiocy retardation retardment simple-wittedness simplemindedness simpleness simplicity subnormality