Ongoing is a synonym of Continuous. Continuous is related to Line. Line can be used for Definition. 
Rain is the opposite of Snow. you are likely to find Snow in/at/on North. North is related to Direction. Direction is related to Back. 
Ongoing <--Synonym--> Continuous <--RelatedTo--> Line --UsedFor--> Definition 
Rain <--Antonym--> Snow --AtLocation--> North <--RelatedTo--> Direction <--RelatedTo--> Back 