Illegal is the opposite of Legal. Legal is related to Plea. Plea is a type of Answer. Answer is related to Guess. 
Group is related to Grain. Grain is related to Little. Little is related to Pale. Pale is related to Loose. 
Illegal <--Antonym--> Legal <--RelatedTo--> Plea --IsA--> Answer <--RelatedTo--> Guess 
Group <--RelatedTo--> Grain <--RelatedTo--> Little <--RelatedTo--> Pale <--RelatedTo--> Loose 