Birthday is the opposite of Death. Death is a type of End. End is a synonym of Purpose. Purpose is a synonym of Intend. 
Send is related to Birthday. Birthday is related to Thing. Unit is a type of Thing. Unit is related to Act. 
Birthday <--Antonym--> Death --IsA--> End <--Synonym--> Purpose <--Synonym--> Intend 
Send <--RelatedTo--> Birthday <--RelatedTo--> Thing <--IsA-- Unit <--RelatedTo--> Act 