Substitutionary, which means acting or serving as a substitute, can be replaced by other words with a similar meaning. Some synonyms for substitutionary include surrogate, alternate, replacement, proxy, deputy, and stand-in. Each synonym has nuances and shades of meaning that distinguish them from one another. Surrogate implies taking the place of another, while alternate suggests a choice between two options. Replacement refers to an object or person that is put in the place of something or someone else. Proxy and deputy imply acting on behalf of another. Stand-in emphasizes the temporary nature of the substitution. When writing, choosing the right synonym can improve the clarity and precision of your message.