Joint is the opposite of Individual. Individual is the opposite of Shared. 
Friendship is derived from Friend. Company is a type of Friendship. Company is created by Founder. Founder is a type of Entrepreneur. 
Joint <--Antonym--> Individual <--Antonym--> Shared 
Friend <--DerivedFrom-- Friendship <--IsA-- Company --CreatedBy--> Founder --IsA--> Entrepreneur 