What term describes failing to carry out a promise or commitment?

The term that describes failing to carry out a promise or commitment is "renege." This word specifically refers to the act of going back on a commitment or promise, indicating that someone has not fulfilled their obligations. It conveys the idea of breaking trust or failing to follow through on what was agreed upon, which is essential in various contexts such as contracts, agreements, and personal relations.

In contrast, the other terms do not relate to this concept. "Prosaic" describes something that is mundane or commonplace, lacking in imagination or creativity. "Pundit" refers to an expert or authority who provides opinions, often in a specific field, and has no connection to commitments. "Propensity" indicates a natural inclination or tendency towards a particular behavior, which does not imply the act of failing to fulfill a promise. Therefore, "renege" clearly encapsulates the idea of failing to carry out a promise or commitment.