The Spanish verb 'igualar' (meaning 'to make equal' or 'to equalize') comes from the Spanish adjective 'igual' ('equal') combined with the verb-forming suffix '-ar'. The word 'igual' itself derives from Latin 'aequalis' meaning 'equal' or 'uniform', which in turn comes from the Latin root 'aequus' meaning 'equal, level, or fair'.

The development from Latin to Spanish shows a typical sound change pattern where the Latin 'ae' became 'i' in Spanish, and the medial 'qu' became 'gu'. The addition of the '-ar' suffix transformed the adjective into a verb meaning 'to make equal' or 'to equalize'.

The most obvious related Spanish word is the simpler adjective 'igual' meaning 'equal' or 'same', which you'll often hear in common phrases like 'igual que' (same as) or '¡igual!' (same here!/likewise!). Another related word is 'igualdad' meaning 'equality', which is formed by adding the noun suffix '-dad' to 'igual'.

English speakers might recognize the connection to words like 'equal', 'equality', and 'equalize', which all come from the same Latin root 'aequus'. The English words maintained spelling closer to the original Latin, while Spanish underwent more sound changes. Another related English word is 'equitable' (meaning fair or just), which also derives from Latin 'aequus'.