Longtime is the opposite of New. New is related to Old. 
Certain is similar to Reliable. Quality can be Reliable. Quality is related to Heavy. Heavy is similar to Harsh. 
Longtime <--Antonym--> New <--RelatedTo--> Old 
Certain <--SimilarTo--> Reliable <--HasProperty-- Quality <--RelatedTo--> Heavy <--SimilarTo--> Harsh 