In contrast to the other Germanic languages, Gothic has two endings in the genitive plural: all masculines and neuters have - ē (e.g. dagē, waúrdē, gastē, suniwē, attanē, haírtanē, brōprē ); of the feminines, some have - ē , some - ō (e.g. qēnē, mahtē, handiwē, baúrgē , but þiudō, tuggōnō, manageinō ). The other Germanic languages have only one ending each: OHG OS - o (e.g. tago, dago ), OIcel. OE - a ( daga ). This ending agrees with Gothic - ō , from Proto-Germanic - õ ( n ). The Gothic ending - ē is unique not only in Germanic but in Indo-European.
Gustav Must (Sun,) studied this question.
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