a person joint with others in work, business or crime

colleague

a close friend (especially used by boys)

friend

a person who goes, or is often or always with, another

helper, friend

a person, not a relation, who one knows and likes well

confidant, companion

a man; one of a pair of birds or animals; a ship's officer (not an engineer) below the rank of captain; a worker who helps another; (to cause birds or animals) to unite for the purpose of producing young

one of a pair; partner

a person who takes a part with another or others in some activity

person who takes part with another