teacher,professor,lecturer,tutor,instructor:
1,A teacher usually works in a school
2,A professor is a teacher of the highest rank in a British university, and is a general term for a teacher in an American college.
3,someone who teachers in a British university and who is not a professor is called a lecturer.
4,A tutor gives lessons to just one student or a small group of students, especially privately in their home or a student's home.
5,An instructor is someone who helps people learn a sport or practical skill, such as driving,skiing,or swimming; (in American)someone who teaches in an American college or university and who has a rank below ASSISTANT PROFESSOR.