The term 'circular opening' can be described by three crossword solutions: SEMI (4 letters), EYEHOLE (7 letters), and LETTERC (7 letters). SEMI is a prefix meaning 'HALF' or 'PARTIALLY, ' and is often used to describe SEMI-circular shapes. An eyehole is a small, circular opening in a door or wall, usually used for viewing or passing items through. Lastly, LETTERC is an abbreviation for 'LETTERBOX, ' which is a receptacle for receiving mail, typically with a circular opening.