deber
must
debt
something owed
+
-er
verb suffix
Deber means must and can be thought of as debt0 (something owed0) + -er1 (verb suffix1), implying an obligation or duty.
verb
  1. must
    To be obliged or required to do something
    Debes hacer tu tarea. // You must do your homework.
noun
  1. duty
    An obligation or responsibility
    Es mi deber ayudar. // It's my duty to help.