To "be a witness" means to observe or see something happening and be able to testify or report back about it. Alternative synonyms for this phrase include "witness firsthand," "witness in person," or "bear witness to". These phrases convey a sense of being present at the scene and having personal experience with what occurred. Other possible synonyms include "observe closely," "vouch for," or "attest to." These words emphasize the importance of reliability and accuracy in the testimony being given. In legal or official settings, it is crucial to have trustworthy witnesses who can provide an honest account of what they saw or heard.