Train is a synonym of String. String is a type of Add. Add is related to Action. Action is related to Bury. 
Might is related to Could. Could is etymologically related to Shall. Should is a form of Shall. 
Train <--Synonym--> String --IsA--> Add <--RelatedTo--> Action <--RelatedTo--> Bury 
Might <--RelatedTo--> Could --EtymologicallyRelatedTo--> Shall <--FormOf-- Should 