The Spanish word 'bulto' comes from the Latin word 'vultus', meaning 'face' or 'countenance'. Over time, the meaning broadened from referring specifically to a face to encompass any three-dimensional form or figure. The initial 'v' in Latin evolved to 'b' in Spanish, a common sound change between these languages. Today, 'bulto' refers to any bulk, mass, or figure - essentially any large or prominent shape, whether it's a package, bundle, or a human figure in the distance.

A related Spanish word is 'bultar', meaning 'to form a bulk or mass', though this verb is less commonly used than 'bulto'. The word 'abultado' (meaning 'bulky' or 'swollen') is also derived from the same root and might be more familiar to Spanish learners.

While English 'vault' might seem related due to its similar sound, it actually has a different etymology. However, the English word 'vulture' does share a distant connection to Latin 'vultus', as both originally referred to appearance or countenance, though 'vulture' developed specifically to refer to the bird's distinctive face and appearance.