The Spanish word 'antagonista' comes from Ancient Greek through Latin. It was formed by combining two Greek elements: 'anti-' meaning 'opposite' or 'against', and 'agonistes' meaning 'fighter' or 'contestant'. These combined to form 'antagonistes' in Greek, meaning 'opponent' or 'rival'. This word was then borrowed into Latin as 'antagonista', and finally made its way into Spanish with the same spelling, where it means 'antagonist' or 'opponent'.

The 'agon-' part in 'antagonista' originally referred to a contest or struggle in Greek, so an antagonist is literally someone who struggles or fights against someone else.

The Spanish word 'agonía' (agony) is related to 'antagonista', as they both come from the same Greek root related to struggle or contest. While 'agonía' refers to the struggle or suffering itself, 'antagonista' refers to someone who causes opposition or struggle against others.

English speakers will recognize many related words: 'antagonist', 'antagonize', and 'antagonistic' all share the same Greek origins. The word 'agony' is also related, coming from the same Greek root 'agon-' meaning struggle or contest. Even the word 'protagonist' follows a similar pattern, where 'prot-' (meaning 'first' or 'chief') replaces 'ant-' (meaning 'against').