Describe is related to Illustrate. Illustrate is a type of Decorate. Decorate is the opposite of Bare. 
Extension is derived from Extend. Extension is related to Finger. 
Describe <--RelatedTo--> Illustrate --IsA--> Decorate <--Antonym--> Bare 
Extend <--DerivedFrom-- Extension <--RelatedTo--> Finger 