Definition from Wiktionary, the free dictionary
Etymology 1 
Form of the verb accidō (“fall upon; befall”).
- third-person plural imperfect active indicative of accidō
- "they were falling down, they were falling upon, they were falling near; they were descending"
- "they were happening (to), they were taking place, they were occurring, they were befalling"
Etymology 2 
Form of the verb accīdō (“fell, cut down; use up; impair”).
- third-person plural imperfect active indicative of accīdō
- "they were beginning to cut into, they were beginning to cut through, they were felling, they were cutting down"
- "they were using up, they were consuming, they were diminishing"
- "they were impairing, they were weakening, they were shattering"