Smoke is related to Dirty. Dirty is related to Coal. Coal is related to Natural. 
Join is related to Attach. Attach is a synonym of Bind. Bond is etymologically related to Bind. Bond is related to Spy. 
Smoke <--RelatedTo--> Dirty <--RelatedTo--> Coal <--RelatedTo--> Natural 
Join <--RelatedTo--> Attach <--Synonym--> Bind <--EtymologicallyRelatedTo-- Bond <--RelatedTo--> Spy 