Sleeper comes from sleep (from Old English slæpan, of Germanic origin) plus the agentive suffix -er. The historical chain includes Old English slæpan. The formation is best read as suffixal and borrowed: the word sleeper carries its older form-history into a compact English lexical shape. In present English it is used as a noun, "one who sleeps, a sleeping car, or an unexpected success". Related English forms include sleep, sleeping, and asleep. The result is a noun whose etymology preserves both the older form and the later English specialization.