The term 'fit harmoniously' can be summarized by the word 'DOVETAIL, ' which is an 8-letter word. Dovetailing is a type of woodworking joint that is used to join two pieces of wood together in a way that is both strong and aesthetically pleasing. The joint is made by cutting each piece of wood into a shape that resembles a dove's tail, hence the name. This type of joint is often used in furniture making and other carpentry projects.