The Spanish verb 'nadar' (to swim) comes from the Latin verb 'natare', which was a frequentative form meaning 'to swim repeatedly' or 'to swim habitually'. 'Natare' itself developed from the simpler Latin verb 'nare', also meaning 'to swim' or 'to float'. The evolution from Latin 'natare' to Spanish 'nadar' shows a common sound change where the 't' became 'd' between vowels, a process called lenition that frequently occurred as Latin evolved into Spanish.

Some related Spanish words include 'nadador' (swimmer), 'nado' (swimming), and 'natación' (swimming as a sport or activity). Notice how some derivatives maintain the original 't' from Latin, especially in more formal or technical terms like 'natación', while others use the 'd' like in 'nadar'.

English words related to 'nadar' include 'natation' (swimming), 'natatorial' (relating to swimming), and 'natant' (swimming or floating in water). These words are less common in everyday English but are used in scientific contexts. They preserve the 't' from the Latin root rather than the 'd' found in Spanish. You might also recognize this root in words like 'natatorium' (an indoor swimming pool).