The term 'CONVERTS INTO LEATHER' can be summarized by the crossword solution 'TANS', which is a four-letter word. Tanning is the process of treating animal skins to convert them into leather. This process involves soaking the skins in a solution of tannin, an acidic chemical compound, and then stretching and drying them. Tanning has been used for centuries to produce leather for clothing, furniture, and other items.