Undeflectable is an adjective that describes something that cannot be turned away or diverted from its course. Some synonyms for undeflectable are impervious, unyielding, and unwavering. Impervious refers to something that is not affected or influenced by external factors. Unyielding describes something that remains firm and resolute in the face of opposition or pressure. Unwavering means that something is steadfast and does not falter or change its direction. Other synonyms include steadfast, immutable, inflexible, and unshakeable. All of these words convey the idea of something that is impossible to sway or alter, making them useful for describing a variety of situations.