The Spanish word 'entonces' (meaning 'then') comes from Old Spanish 'entonce', which developed from the Vulgar Latin '*intunce'. This Vulgar Latin form was created by combining two Latin elements: the prefix 'in-' (meaning 'inward') and 'tunc' (meaning 'then'). Over time, the pronunciation and spelling evolved from '*intunce' to 'entonce' and finally to the modern Spanish 'entonces', while maintaining its temporal meaning of 'then' throughout these changes.

While 'entonces' is already one of the most basic and commonly used Spanish words for expressing time relationships, it's worth noting that it stands somewhat alone in modern Spanish, without many obvious cognates. This is because the Latin elements that formed it ('in-' and 'tunc') didn't produce many other surviving descendants in Spanish.

While English doesn't have any direct cognates of 'entonces', we can find some connection through the Latin prefix 'in-', which appears in many English words like 'inside', 'inward', and 'internal'. However, the Latin 'tunc' (then) took a different path in English, which instead uses words derived from Old English sources for this concept.