The Spanish word 'seno' comes from the Latin word 'sinus', which meant 'curve, cavity, or bay'. In Spanish, the word evolved to mean 'breast' or 'cavity', maintaining the original sense of a curved or hollow space. The mathematical meaning 'sine' also developed from this same root, as it relates to the curved nature of the trigonometric function.

The Spanish word 'ensenada' (meaning 'cove' or 'bay') is related to 'seno', as it incorporates the same Latin root 'sinus'. Both words maintain a connection to the concept of a curved or hollow space, with 'ensenada' specifically referring to a curved indentation in a coastline.

Several English words are related to 'seno' through the Latin 'sinus'. The most direct cognate is 'sinus', as in the anatomical air-filled cavities in the skull, which preserves the Latin meaning of 'cavity'. The mathematical term 'sine' is also related, having developed from the same Latin root. The word 'insinuate' (to suggest indirectly) also comes from this root, originally referring to following a winding path.