Afraid is the opposite of Brave. Brave is the opposite of Fear. 
Gentle is a type of Pet. Bird can Pet. Bird is related to Living. Living is related to Household. 
Afraid <--Antonym--> Brave <--Antonym--> Fear 
Gentle --IsA--> Pet <--CapableOf-- Bird <--RelatedTo--> Living <--RelatedTo--> Household 