The Spanish word 'horno' meaning 'oven' comes directly from the Latin word 'furnus', which also meant 'oven'. The initial 'f' in Latin changed to 'h' in Spanish, which is a common sound change that occurred in many Spanish words derived from Latin (like 'hijo' from Latin 'filius'). This sound change, known as f- to h-, is one of the characteristic features of the development from Latin to Spanish.

Some related Spanish words include 'hornear' (to bake), 'hornada' (batch of baked goods), and 'hornilla' (stove burner). All these words maintain the connection to heating and cooking that was present in the original Latin word.

While English 'oven' is not related to 'horno', there are some English words that come from the same Latin root 'furnus'. These include 'furnace', which preserves the original 'f' sound and refers to a device for heating, and 'inferno', which relates to intense heat. The word 'furnish' also comes from this root, though its meaning has evolved from the original sense of 'providing warmth' to the more general sense of 'providing' or 'supplying'.