Michael Inwood's dictionary on Ereignis and other happenings.
event, happening, occurrence 1. The most general term for an event is Ereignis, from sich ereignen, 'to happen, occur'. The words come from Auge, 'eye', and were until the eighteenth century spelt Eräugnis, eräugnen, lit. 'placing/to place before the eye, becoming/to become visible' -- as Heidegger knew (OWL, 260/129). Heidegger also uses, Ereignung (Eräugnung), 'event(uating)', which is similar to Ereignis, but more verbal. The words became associated with (sich) eignen, 'to be suitable, belong', anereignen, 'to appropriate', and eigen, '(one's) own', since some dialects pronounced äu as ei. 2. Begebenheit, 'event', comes from begeben, 'to issue, put [coins, etc.] in circulation' and sich begeben, 'to betake oneself; expose oneself [to danger]; to come to pass'. It is 'often, but not necessarily, something out of the ordinary' (DGS, 110). 3. Vorgang, from vorgehen, 'to proceed, go on, happen', is 'something changing, evolving, a process. The plural is used of a vague, undefined series of happenings. It thus contrasts with the specific term Ereignis' (DGS, 111). 4. Geschehnis, 'event, incident, happening', is from geschehen, originally 'to hurry, rush on, run', but now 'to happen'. It is 'the most abstract term for "happening". Its use is confined to the written word' (DGS, 111). The nominalized infinitive is also used for 'happening(s), event(s)'. 5. Vorkommnis(se), 'occurrence(s)', from vorkommen, 'to come forth, occur, etc.', is a 'happening that concerns a person' (DGS, 111).