Discuss describes typical conversation in which you can present your ideas in peace. Argue means speak to someone but being angry with him. So argue could be some kind of discussion but in bad atmosphere.

rob means steal but often using violence: The terrorists financed themselves by robbing banks. steal is more general and means to take smth without permission: The number of cars which are stolen every year has risen.

For single words like these you might want to try a dictionary.

If you rent smth you pay for it regularly. Hire means to pay for smth for a short period.