Accusation is etymologically related to Accuse. Allegation is a type of Accusation. Allegation is a type of Claim. Claim is related to Report. 
Beach is related to Tide. 
Accuse <--EtymologicallyRelatedTo-- Accusation <--IsA-- Allegation --IsA--> Claim <--RelatedTo--> Report 
Beach <--RelatedTo--> Tide 