The word 'theft' originates from the Old English 'þēofþ', 'þȳfþ', or 'þīefþ', which meant 'stealing'. These forms were themselves derived from the Proto-Germanic 'þiubiþō', a noun built from the root 'þeubaz', meaning 'thief'. This Germanic root is further traced back to the Proto-Indo-European 'tewp-', meaning 'to swell', which conceptually evolved to imply the sense of 'to be puffed up with pride' and, by metaphorical extension, 'to be secretive or covert'. The semantic journey from 'swelling' to 'stealing' likely passed through the idea of clandestine or furtive behavior. The modern abstract meaning, denoting the general action or crime, has remained remarkably stable from its ancient Germanic origins.

The word 'theft' is a simplex word derived from a single, indivisible Old English root. It is not productively formed from separate, identifiable morphemes in modern English.