The term 'OLD LETTER OPENER' can be broken down into two crossword solutions: SIRS (4 letters) and SIR (3 letters). A letter opener is a tool used to open envelopes, typically made of metal or plastic. It is also known as a paper knife. Historically, letter openers were often ornate and made of silver or other precious metals. They were often given as gifts to important people such as knights, which is why the crossword solutions include the word 'SIR'.