Pigeon-chested is often used to describe someone with a narrow, hollow chest. However, there are many other ways to describe this physical attribute. Some possible synonyms include flat-chested, narrow-chested, hollow-chested, concave-chested, sunken-chested, and shallow-chested. Additionally, you could use more creative descriptions such as sparrow-chested, bird-chested, or even peanut-chested. The key is to use descriptive language that accurately portrays the physical appearance without being overly derogatory or offensive. By using synonyms for pigeon-chested, you can add variety and depth to your writing and better express your intended meaning.