It is always good with such questions that ask you to explain the meaning of a quote to look at the quote in context and see what happens before and after it to try and see if any contextual clues will give you an idea as to what it means. If we do this, we see that Oliver calls Orlando a "villain" in Act I scene 1 of this play after an argument between them in which Orlando complains that Oliver has not given him the education and upbringing that his father desired he should have. As the argument gets gradually more and more heated, it is clear that, although Oliver is older and has the power and money, Orlando is stronger than he is and is able to convincingly show his superiority through fighing with him. Orlando, exasperated with his brother and his attitude towards him, thus moves to handle him and wrestle with him. It is at this stage that Oliver calls his brother a villain, saying:
Wilt thou lay hands on me, villain?
Thus the word indicates the distance and enmity between the brothers, introducing us with a fraternal relationship which is in need of reconciliation, just as we will soon hear about another fraternal relationship in need of reconciliation.
Oliver complains about the shabby manner in which he is treated by oliver,disregarding their fathers will.Orlando says that Oliver does not take care of his education and his codition is no better than that of a rustic or an ox in the farmyard.Even olivers horses are maintained well. I the absence of a good upbriging, orlando is losing the talents he has been enowed with by nature. As a consequence of ill-treatment. orlando has become rebellious, his spirit has begun to revolt against his elder brother.Oliver meanwhile appears in scene.Orlando confronts him and accuses him of not doing his duty which their late father had entrusted upon him.Oliver becomes furius of the accusatin and slaps orlando calling him a villian.