Normal is a synonym of Usual. Usual is related to Custom. 
Starter is related to Spark. Spark is related to Electrical. Electrical is related to Motor. Motor is related to Electric. 
Normal <--Synonym--> Usual <--RelatedTo--> Custom 
Starter <--RelatedTo--> Spark <--RelatedTo--> Electrical <--RelatedTo--> Motor <--RelatedTo--> Electric 