"Stay up for" is a phrase that means to remain awake until a certain time or event. It is often used in casual conversations and can be substituted with different synonyms depending on the context. Some synonyms for "stay up for" include "wait up for," "keep vigil," "remain awake," "stand watch," "be alert," "be wakeful," or "keep one's eyes open." These synonyms can be used in various scenarios, such as waiting for someone to arrive, keeping watch over a sick family member, or waiting for an important phone call or email. No matter which synonym you choose to use, it is important to stay alert and conscious until the designated time or event has passed.