Happy is the opposite of Sad. Sad is related to Tragedy. Tragedy is related to Disaster. 
Crowd is related to Show. Define is a type of Show. Define is related to Explain. Explain is related to Justify. 
Happy <--Antonym--> Sad <--RelatedTo--> Tragedy <--RelatedTo--> Disaster 
Crowd <--RelatedTo--> Show <--IsA-- Define <--RelatedTo--> Explain <--RelatedTo--> Justify 