die Verbindlichkeit
Binding force. Duden’s example is diese Regel hat für mich keine Verbindlichkeit, this rule does not bind me. In business language, the plural Verbindlichkeiten means debts. Verbindlichkeiten eingehen means to take on debts.
die Zusage
Duden gives two meanings. It is a positive answer to an invitation. It is also an assurance that one will act as the other person wishes in a certain matter.
versprechen
To promise.
sich versprechen
To make a slip of the tongue. Duden defines it as saying something other than one intended. With sich, the verb for a promise names a word that came out wrong.