The Spanish verb sonreír ('to smile') comes from the Latin verb subridere, which meant 'to smile'. The Latin subridere was formed by combining two parts: the prefix sub- meaning 'under, from below' and the verb ridere meaning 'to laugh'. This combination literally suggested the idea of 'laughing a little' or 'laughing under/slightly', which evolved to mean 'to smile'. The Latin sub- prefix evolved into son- in Spanish, while ridere became -reír, giving us the modern Spanish word sonreír.

The Spanish verb reír ('to laugh') is directly related to sonreír, as it comes from the same Latin root ridere. While reír maintains the basic meaning of 'to laugh', sonreír specifically refers to the gentler action of smiling, maintaining the idea of a 'smaller' or 'lesser' laugh that the original sub- prefix suggested.

While English 'smile' is not related to sonreír, we can find related English words that come from the same Latin ridere, such as 'ridiculous' (something laughable), 'deride' (to laugh at mockingly), and 'risible' (capable of provoking laughter). These words all maintain a connection to the concept of laughter, though they've developed more specific meanings over time.