The Spanish verb 'aguar' (meaning 'to water down' or 'to dilute') comes from combining the Spanish noun 'agua' (meaning 'water') with the common Spanish verb suffix '-ar'. The noun 'agua' itself derives from the Latin word 'aqua', meaning 'water'. This is a straightforward etymology where the meaning has remained closely tied to the concept of water, with the verb form specifically referring to the action of adding water to something to dilute it.

The most obvious related Spanish word is 'agua' (water), which is much more common and fundamental to learn. Other related words include 'acuático' (aquatic), 'acuario' (aquarium), and 'aguacero' (downpour). All these words share the same Latin root 'aqua' and maintain connections to the concept of water.

English speakers can connect 'aguar' to several familiar English words that come from the same Latin root 'aqua', such as 'aquatic', 'aquarium', 'aqueduct', and 'aqueous'. The Latin 'aqua' is also preserved directly in many English scientific and technical terms. Understanding this connection can help remember that 'aguar' is related to water, specifically the action of adding water to something.