“mucallim” (معلم) generally refers to a primary-school teacher. It comes from the word “callama” (علٌم) which means “to transmit knowledge.”

“mudarris” (مدرس) is a more general word for teacher, and a mudarris can refer to a language teacher, a person who teaches a specific skill, etc. It comes from the verb “darrasa” (درٌس) which means “to give lessons.”

Another word I can add to your vocabulary is ‘ustaadh / ‘ustaadha (أستاذ). And this means “professor.” It is used when talking about high school and university teachers.