Hair's-breadth is a term used to describe something that is extremely close or narrow. While it's a vivid and descriptive term, there are many other synonyms you can use to convey a similar meaning. Words like "razor-thin", "paper-thin", "wafer-thin", and "microscopic" all work well and add an extra layer of detail to your writing. Other options include "thread-like", "fine", "thin as a sheet of paper", and "narrow as a whisker". By using synonyms for hair's-breadth, you can enliven your writing, make it more interesting, and help your readers better understand just how close something is to happening or not happening.