Flesh is a synonym of Fat. Fat is the opposite of Health. Health is related to Doctor. Doctor is related to Heal. 
Mere is a synonym of Simple. Single is etymologically related to Simple. 
Flesh <--Synonym--> Fat <--Antonym--> Health <--RelatedTo--> Doctor <--RelatedTo--> Heal 
Mere <--Synonym--> Simple <--EtymologicallyRelatedTo-- Single 