A very close and intimate friend.
Somebody's alternate personality or persona; another self.
A corporation used by a person to conduct personal business in an attempt to shield himself or herself from personal liability, and which a court may penetrate by "piercing the corporate veil" to impose liability on the person when they commit fraud or injustice.
A friend, buddy, mate, cobber; someone to hang around with.
An informal term of address, often used ironically in a hostile way.
Be friends with, hang around with.