Clean is a synonym of Blank. Blank is etymologically related to Blind. Blind is related to Date. 
Normal is the opposite of Ill. Ill is the opposite of Ok. Ok is a synonym of Cool. Cool is related to Like. 
Clean <--Synonym--> Blank --EtymologicallyRelatedTo--> Blind <--RelatedTo--> Date 
Normal <--Antonym--> Ill <--Antonym--> Ok <--Synonym--> Cool <--RelatedTo--> Like 