One way to hold this word: it is a label that points at epilepsy and says this one belongs there. Point it at an attack and you get an epileptic seizure — out of all the reasons a person might fall or shake, this is the one. Point the same label at a person and it becomes a noun, an epileptic. The word itself does not change; only what it is pinned to changes, and that is worth noticing, because pinning it to a person names them by the condition alone.
The packet's source entry says the word comes from Ancient Greek epilēptikós, the adjective belonging to epilepsy. That is why the adjective is the older and plainer job, and why the noun reads as the adjective used to stand for a person.
來源資料說這個字來自古希臘文 epilēptikós，是屬於 epilepsy 的形容詞。這也說明為什麼形容詞是它比較根本的工作，而名詞用法讀起來像是形容詞被拿來代表一個人。
Wiktionary entry for epileptic supplied in evidence packet (kaikki:3f6f69a190036ae4:695225371), From Ancient Greek ἐπιληπτικός
One branch
指向癲癇的那張標籤
兩個用法其實是同一張標籤，差別只在貼在發作上，還是貼在人身上。
adjective · B2
Caused by epilepsy, or connected with it. Epilepsy is a long-term condition of the brain in which a person has sudden attacks, called seizures or fits, when the body may shake and the person may lose consciousness for a short time.
癲癇的、癲癇引起的