The term 'ONE WHO BREAKS INTO A VAULT' can be summarized as a SAFECRACKER, which is an 11-letter word. A SAFECRACKER is someone who specializes in opening locked containers, such as safes and vaults, without the use of a key or combination. Safecrackers are often employed by law enforcement agencies to gain access to evidence or other items that are locked away. They may also be hired by private individuals or businesses to open safes that have been forgotten or lost the combination.