The Spanish word 'sesenta' meaning 'sixty' comes from the Old Spanish 'sessaenta', which in turn derives from the Latin word 'sexaginta' (also meaning 'sixty'). The evolution from Latin to modern Spanish shows typical sound changes, where the Latin 'x' sound (pronounced like 'ks') simplified to 's', and the 'gi' combination evolved to become just 'e'. This made the word easier to pronounce while maintaining its numerical meaning.

The Spanish word 'seis' (meaning 'six') shares the same Latin root, as 'sexaginta' is essentially formed from 'sex' (six) with a suffix to create the meaning 'sixty'. This connection makes it easier to remember that 'sesenta' relates to 'six' times ten.

English words related to 'sesenta' include 'sexagenarian' (a person in their sixties) and 'sexagesimal' (relating to the number sixty or a system based on it). These words preserve the original Latin 'sex-' prefix more clearly than the Spanish word does. The English word 'six' is also distantly related, coming from the same Indo-European root that gave Latin 'sex'.