paniko

No -ik- suffix. Esperanto has -ism- and -ist- and a dozen other live affixes, and it does not have -ik-. The ending turns up in muziko, publiko, fabriko, politiko, kritiko and here, always because the Greek or Latin word arrived with it already fused on. Panik- is one root. If you try to lever it apart you are left with pan-, which in Esperanto is bread.

The gift inside the word. Pan was the god of woods, flocks and empty hillsides, half goat, and the Greeks explained a very specific experience with him: the terror that comes over animals and people in a lonely place for no reason anyone can point to. That is panikos deima, Pan-fear, and it is the whole word. Two things follow that are worth carrying. First, panic in the original sense is groundless and sudden, not merely intense - which is exactly how the Esperanto word is used. Second, the goat is not a coincidence: Pan's legs put him beside kapro, which arrives four ranks later in this same chapter, and both words are in the language because Greek shepherds needed them.

Building on it. Panikiĝi is to get into a panic, panikigi is to throw someone else into one, and the adjective is panika. The plain contrast to hold on to is trankvila: the calm you lose.