Ser de palabra or tener palabra, to be a person of one’s word. The Diccionario del español de México defines it as “ser leal, honrado y cumplido” (to be loyal, honest and dutiful).
Cumplido describes a person who meets obligations. As a noun, it also means a compliment. Empeñar la palabra, to pledge one’s word. De palabra, said but not set down in writing. Faltar a su palabra, to break a promise.