Real Dictionary

tutor
countable noun: A tutor is a teacher at a British university or college. In some American universities or colleges, a tutor is a teacher of the lowest rank.
countable noun: A tutor is someone who gives private lessons to one pupil or a very small group of pupils.
verb: If someone tutors a person or a subject, they teach that person or subject.

tutor in American English
a teacher who gives individual instruction to a student; private teacher
to act as a tutor to; teach; esp., to give individual instruction to
to act as a tutor, or instructor
intransitive verb: to act as a tutor or private instructor
noun: a person employed to instruct another in some branch or branches of learning, esp. a private instructor
transitive verb: to act as a tutor to; teach or instruct, esp. privately

tutor in British English
noun: a teacher, usually instructing individual pupils and often engaged privately