The phrase "leaves straight and narrow" refers to someone who strays from the path of righteousness and morality. There are many synonyms for this phrase that can be used to describe someone who veers off course. Some possible synonyms include "deviates from the right path," "wanders astray," "goes off track," "loses their way," "strays from the path of virtue," and "falls from grace." Other common synonyms include "backslide," "backslip," "fallen from favor," and "fall off the straight and narrow." Regardless of the synonym used, the phrase "leaves straight and narrow" conveys the idea of a person who has lost their way and is no longer following a moral and upright path.