The Spanish word 'tribu' (meaning 'tribe') comes from the Latin word 'tribus', which originally meant 'a division of three' or 'tribe'. The Latin word itself is a combination of two elements: 'tri-' meaning 'three', and '-bus', which was a dative plural suffix in Latin. This etymology reflects how early Roman society was traditionally divided into three original tribes.

Several common Spanish words share the 'tri-' root meaning 'three', such as 'tres' (three), 'triángulo' (triangle), 'triple' (triple), and 'trimestre' (trimester). These words all preserve the connection to the concept of 'three' that was present in the original formation of 'tribu'.

The English word 'tribe' is directly related to Spanish 'tribu', as both come from Latin 'tribus'. Other English words sharing the 'tri-' element include 'triple', 'triangle', and 'trinity', all preserving the original meaning of 'three'. The connection between 'three' and 'tribe' might seem unusual today, but it reflects the ancient Roman social organization into three distinct groups.