Lightning is related to Bright. Bright is a synonym of Promising. Promising is a form of Promise. Promise is a type of Expectation. 
Slight is the opposite of Significant. Significant is a synonym of Massive. 
Lightning <--RelatedTo--> Bright <--Synonym--> Promising --FormOf--> Promise --IsA--> Expectation 
Slight <--Antonym--> Significant <--Synonym--> Massive 