the sage's grandson where the 'maou' the people use to call him use the ma in reference to magic (mahou) i.e. 'magic king/lord' for his OP magic, but him being a reincarnated person clearly imagine the 'demon lord' meaning and get the cringes when he get called that...
a different series give furigana for maou as "Evil Lord", another possible translation of the ma in that one (in that one actual demons exist and they use 'akuma'...with a 'devil' being higher evolution among them...so yeah)