The Spanish word 'ventanilla' comes from 'ventana' (meaning 'window') with the diminutive suffix '-illa' added to indicate a small window. The word 'ventana' itself derives from the Latin word 'ventus', meaning 'wind'. This etymology reflects how windows were originally conceived as openings to let wind and air flow through a building.

The most obvious related Spanish word is 'ventana' (window), from which 'ventanilla' is directly derived. Another common related word is 'viento' (wind), which comes from the same Latin root 'ventus'. The connection between these words helps tell the story of how windows were historically viewed as sources of ventilation in buildings.

Several English words share the same Latin root 'ventus'. The most notable ones are 'ventilate' and 'ventilation', which directly relate to the movement of air. The word 'vent' also comes from this root, maintaining the original connection to the concept of air flow. Understanding this connection can help remember that 'ventanilla' refers to a small opening or window.