agon

The root agon comes from Greek agōn, which originally named a public gathering — and especially the contest held at it. The great athletic festivals like the Olympics were agōnes: places where competitors fought, raced, and wrestled in front of a crowd. From this single image of a public struggle, the whole family grows.

The key figures of any contest gave us our most literary words. The chief competitor — the one standing first in the arena — was the prōtos agōnistēs: prōtos (first) + agōnistēs (contestant). That fused into protagonist, the 'first contestant.' When Greek drama borrowed the word, the protagonist became the lead actor, and today it means the main character of any story. The one fighting against him was the ant-agōnistēs: anti (against) + agōnistēs = antagonist, the opponent. From this came antagonism (the state of being in opposition) and the verb antagonize (literally 'to make into an opponent,' hence 'to provoke into hostility').

Greek also had a darker sibling, agōnia, formed from the same root. If agōn was the contest, agōnia was the extreme exertion and strain of fighting in it — the writhing struggle of an athlete pushed to the limit. That sense of violent struggle slid easily into the meaning of mental and physical suffering. So agony came to mean intense pain, and the verb agonize means to writhe in that struggle: to suffer greatly, or to wrestle painfully with a hard decision (to agonize over a choice).

The pattern across the family: agon is always a fight. With prefixes it tells you who is fighting — pro(t)- the one in front, anti- the one against. On its own (through agōnia) it tells you how it feels to fight: the strain, the struggle, the agony.