Sign is a synonym of Signal. Signal is a type of Electricity. Electricity is related to Spark. 
Retire is related to Rest. Relax requires Rest. Think requires Relax. Think is a synonym of Conceive. 
Sign <--Synonym--> Signal --IsA--> Electricity <--RelatedTo--> Spark 
Retire <--RelatedTo--> Rest <--HasPrerequisite-- Relax <--HasPrerequisite-- Think <--Synonym--> Conceive 