"Serves stead" is a phrase that means "to act as a substitute" or "to take the place of". There are several synonyms for this phrase, including "stands in for", "fills in for", "replaces", "substitutes for", and "takes over for". These phrases are commonly used when discussing someone or something that is taking on the responsibilities or duties of another person or object. For example, a backup quarterback who takes over for the injured starter "serves stead" for him. Similarly, an emergency generator that replaces the primary power source "serves stead" for it. Overall, these synonyms are useful in helping to clearly communicate the idea of substitution or replacement.