The Spanish word 'onda' meaning 'wave' comes directly from the Latin word 'unda', which also meant 'wave'. This is a straightforward etymology where the Latin 'u' sound shifted to 'o' in Spanish, a common sound change in the development from Latin to Spanish.

Some related Spanish words include 'ondear' (to wave), 'ondulado' (wavy), and 'ondulación' (undulation). All these words maintain the core meaning related to waves and wave-like motion.

Several English words share the same Latin root 'unda', including 'undulate' (to move in waves), 'abundance' (originally meaning 'overflowing like waves'), and 'inundate' (to flood or overwhelm, literally 'to come in waves'). The word 'surround' also contains this root, as it originally meant to 'overflow on all sides like waves.'