Essential is a synonym of Natural. Natural is related to Rock. Rock is a different concept from Metal. 
Top is related to High. Hip is etymologically related to High. Hip is part of Thigh. 
Essential <--Synonym--> Natural <--RelatedTo--> Rock <--DistinctFrom--> Metal 
Top <--RelatedTo--> High <--EtymologicallyRelatedTo-- Hip --PartOf--> Thigh 