The term 'PERFORM IN A CHORUS' can be solved by the four-letter word 'SING'. Singing in a chorus is an activity that has been around for centuries, and involves multiple people singing together in harmony. It is often used in musical performances, such as operas, choirs, and musicals. Singing in a chorus requires a great deal of practice and skill, as each singer must be able to match their voice to the other singers in order to create a unified sound.