The term 'stealthy thief' can be described by two crossword solutions: 'PILFERER' (8 letters) and 'catburglar' (10 letters). A PILFERER is someone who steals small amounts of goods, usually without being noticed. A catburglar is a thief who specializes in breaking into buildings, often using stealth and agility to avoid detection. Both terms refer to people who take something without permission, but the catburglar is more likely to be successful due to their skill set.