From ofer- +‎ gān. Cognate with Old High German ubargān.

• IPA^(key): /ˌo.ferˈɡɑːn/, [ˌo.verˈɡɑːn]

ofergān

1. to overspread, overrun, conquer, be over anything, come upon, attack; onfall
   • Homilies of the Anglo-Saxon Church

     Þæt eahtoðe wīte wæs, þæt gærstapan oferēodon eall þæt land swilċe swā næfre ǣrðan nǣron, ne eft næfre ne ġewurðað; and hī forgnogon swā hwæt swā sē hagol belǣfde, oððe on trēowum oððe on ōðrum wæstmum.

     The eight plague was that locusts overran the entire land as they never had before, and never wood again; they gnawed up anything that the hail had left, either on trees or on other plants.

2. to go or pass over a limit, transgress
3. to go across, traverse, pass off or away, come to an end

• Middle English: overgon
  • English: overgo