na-adjective, noun
ignorant; unenlightened; uncivilized
Describes a state of lacking knowledge, culture, or enlightenment; often used in formal or literary contexts to criticize backwardness or ignorance.
彼の蒙昧な態度には呆れてしまった。
I was appalled by his ignorant attitude.
蒙昧な社会では迷信がはびこる。
Superstitions thrive in an unenlightened society.
無知 is a more common and neutral word for ignorance or lack of knowledge, while 蒙昧 carries a stronger literary and judgmental nuance of being uncivilized or unenlightened.
未開 means 'uncivilized' or 'primitive' and often refers to societies or regions, whereas 蒙昧 can describe individuals or mental states as well.
The word is composed of 蒙 (もう, 'darkness, ignorance') and 昧 (まい, 'dark, foolish'), both carrying the sense of obscurity or lack of clarity. The combination reinforces the idea of being in the dark mentally or culturally.