The Spanish verb 'ondular' (meaning 'to wave' or 'to undulate') comes from the Latin word 'unda' meaning 'wave'. This developed into the diminutive form 'undula' meaning 'small wave' in Latin. When this root came into Spanish, it was combined with the verbal suffix '-ar' to create the verb 'ondular', with the 'u' changing to 'o' as often happens in the evolution from Latin to Spanish words.

Several common Spanish words share this wavy origin, including 'onda' (wave), 'ondulado' (wavy, undulating), and 'ondulación' (undulation, wave). You might see 'ondulado' used to describe wavy hair or rippling water.

English speakers might recognize this root in words like 'undulate' (to move in waves), 'abundance' (originally referring to waves flowing over), and 'inundate' (to flood or overwhelm, literally 'to flow in waves'). The word 'redundant' also comes from this root, originally meaning 'overflowing' like waves.