Na-adjective (keiyodoshi), Noun
serious; not joking; straight
ColloquialAbbreviationsee 真面目see まじめ・1
「・・・おい・・・おい、先生!」「え?・・・あ、ああ」「マジだいじょうぶ?休講にしたら?」
"...Hey...Hey, teacher!" "Eh? Oh." "Are you really OK? Shouldn't you cancel the lesson?"
Also written マジmaji、まぢmaji、マヂmaji