Stealer is from the verb 'steal' (Old English 'stelan', to take wrongfully) plus the agentive suffix '-er'. Important recorded forms include stelan (Old English) and *stelaną (Proto-Germanic). Morphologically, the word preserves a built structure whose named elements carry the historical sense into English. The modern sense continues the older lexical line without requiring a separate origin. In current use it covers a person who steals; a thief. The wider family includes related words such as steal, stealth, and stolen.