ichidan verb, intransitive verb
to be conceited; to be arrogant
Archaic intransitive verb. In modern Japanese, this meaning is usually expressed with うぬぼれる, 思い上がる, or 慢心する. The form 慢ずる (まんずる) is a related older variant.
See also: 慢ずる
In old texts, 慢じる is sometimes used to mean 'to be conceited'.