The phrase "gutter out" can mean a variety of things, including losing power, failing, or petering out. Depending on the context, there are several synonyms that can be used to convey this same meaning. For example, if someone's enthusiasm or interest fizzles out, it may be described as waning or subsiding. Additionally, if a fire loses its flame or goes out entirely, it could be said to extinguish or flicker out. Similarly, if a machine or device stops working altogether, it could be described as malfunctioning, breaking down, or failing. Regardless of the specific synonym chosen, all convey a sense of something once active or alive coming to a stop or ending.