The Spanish word 'peli' is a shortened, colloquial form of 'película' meaning 'movie' or 'film'. The word 'película' comes from the Latin word 'pellicula' meaning 'thin skin', which itself derives from the Latin word 'pellis' meaning 'skin'. This etymology reflects how early photographic and motion picture film was made using thin, skin-like layers of material coated with light-sensitive chemicals. Over time, the word came to refer to the movies themselves rather than just the physical film material.

The most closely related Spanish word is 'película', which is the full form of 'peli'. While 'peli' is more casual and colloquial, 'película' is the standard word for 'film' or 'movie' in Spanish. You might also encounter 'película' used to describe any thin layer or membrane, staying closer to its original Latin meaning.

Several English words share the same Latin root 'pellis' (skin). The word 'peel' comes from this root, as does 'pellicle' (a thin film or membrane). The technical term 'pellagra' (a vitamin deficiency disease affecting the skin) also derives from this Latin root. Most notably, the word 'film' itself, while not etymologically related, underwent a similar semantic development - from meaning a thin layer to referring to motion pictures.