Negotiation is derived from Negotiate. Negotiation is a synonym of Dialogue. Dialogue is related to Talk. Talk is related to Speak. 
Contend is a synonym of Debate. Debate is a synonym of Argue. Argue is related to Dispute. Gap is a type of Dispute. 
Negotiate <--DerivedFrom-- Negotiation <--Synonym--> Dialogue <--RelatedTo--> Talk <--RelatedTo--> Speak 
Contend <--Synonym--> Debate <--Synonym--> Argue <--RelatedTo--> Dispute <--IsA-- Gap 