Competitor is a synonym of Opponent. Opponent is the opposite of Friend. Friend is related to Relationship. 
Virus is a type of Species. Species is related to Class. Class is related to Lecture. 
Competitor <--Synonym--> Opponent <--Antonym--> Friend <--RelatedTo--> Relationship 
Virus --IsA--> Species <--RelatedTo--> Class <--RelatedTo--> Lecture 