Mutual is related to Exchange. Exchange is a synonym of Rally. 
Could is etymologically related to Will. Will is related to Slope. Slope is related to Decent. Decent is a synonym of Nice. 
Mutual <--RelatedTo--> Exchange <--Synonym--> Rally 
Could --EtymologicallyRelatedTo--> Will <--RelatedTo--> Slope <--RelatedTo--> Decent <--Synonym--> Nice 