The term 'sinewy and lean' can be described by the word 'WIRY', which is a four-letter word. WIRY is an adjective that describes someone or something that is thin, muscular, and strong. It is often used to describe people who are physically fit and have a toned physique. This term is also used to describe animals, such as horses, that have a slender and muscular body. In general, WIRY is used to describe something that is thin, yet strong and powerful.