Mess is etymologically related to Mission. Mess is related to Crowd. Crowd is related to Gathering. 
Affair is a synonym of Involvement. Involvement is a synonym of Engagement. Engagement is a synonym of Appointment. Appointment is a type of Decision. 
Mission <--EtymologicallyRelatedTo-- Mess <--RelatedTo--> Crowd <--RelatedTo--> Gathering 
Affair <--Synonym--> Involvement <--Synonym--> Engagement <--Synonym--> Appointment --IsA--> Decision 