A deaconess is a woman doing deacon’s work in some Christian churches: a role just below a priest where that ranking exists, or a woman set apart to serve — visiting, teaching, care, and sometimes nursing or charity work. The word is simply deacon with an old ending that marked a woman. Though actually, churches do not agree on the word any more. Some still say deaconess with pride. Others now call women deacons, and deaconess sounds old-fashioned to them, the way actress still exists beside actor. Neither habit is “wrong”; it is church custom. You will meet the word in older books, in some Protestant and Orthodox settings, and in churches that kept a separate women’s ministry. It is church English, not everyday street English.