The Spanish word 'diamante' (meaning 'diamond') has its origins in Ancient Greek. It comes from the Greek word 'adamas' meaning 'invincible' or 'diamond', which was formed from the prefix 'a-' meaning 'without' and 'damas' meaning 'tamed' - literally describing something that cannot be tamed or subdued.

This Greek word was borrowed into Latin as 'adamas', keeping its meaning of 'diamond'. In Vulgar Latin, the word evolved into 'diamas', and finally entered Spanish as 'diamante'. The change from 'a-' to 'di-' at the beginning of the word occurred during the transition through Vulgar Latin, though the word maintained its connection to the precious stone throughout its evolution.

The word 'diamante' is one of the most common forms of this word in Spanish, and while there are related adjectives like 'diamantino' (diamond-like), the base word 'diamante' itself is the primary form used in everyday Spanish.

English speakers will easily recognize the connection between Spanish 'diamante' and English 'diamond'. Both words share the same Greek ancestry through 'adamas'. The English word took a slightly different path through Old French 'diamant', but ultimately comes from the same source meaning 'invincible' or 'untameable'. The word 'adamant' (meaning stubborn or unshakeable) is also related, being a more direct borrowing from the Latin 'adamas' and retaining more of the original 'untameable' meaning rather than the precious stone meaning.