Keeping vigil is a phrase that refers to the act of staying awake and being watchful. While there aren't many direct synonyms for this phrase, some similar phrases can be used in its place. For example, "watching over," "monitoring," or "standing guard" can all convey a similar meaning. Other phrases that could be used include "keeping a lookout," "maintaining vigilance," or "staying alert." Ultimately, any phrase that conveys a sense of being awake and watchful can be used as a synonym for keeping vigil. Regardless of the specific phrase used, the idea is to stay focused and alert to any potential dangers or threats.