
1) Donegal lake 2) Sacred lake in Donegal
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https://www.crosswordclues.com/clue/derg

The Derg, Common Derg or Dergue (Ge`ez: ደርግ, meaning `committee` or `council`) is the short name of the Coordinating Committee of the Armed Forces, Police, and Territorial Army that ruled Ethiopia from 1974 to 1987. It took power following the ousting of Emperor Haile Selassie I. Soon after it was established, the committee was formally...
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http://en.wikipedia.org/wiki/Derg

Derg is a cultivated variety of potato.
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http://www.probertencyclopaedia.com/browse/QD.HTM

HMS Derg was a British River Class frigate of 1460 tons displacement launched in 1943. HMS Derg was powered by two Admiralty 3-drum type boilers providing a top speed of 20 knots. She carried a complement of 140 and was armed with two 4-inch dual-purpose guns; ten 20 mm anti-aircraft guns and one Hedgehog multiple spigot mortar.
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http://www.probertencyclopaedia.com/browse/RD.HTM

Formed in June 1974 and composed of a substantial body of young military officers, none above the rank of major, drawn from the main units of the army, air force, navy, and police. The Derg's membership ranged from perhaps 106 to 120 or more. New officers were never admitted, whereas original members were continuously eliminated, especially during ...
Found on
https://www.photius.com/countries/ethiopia/glossary/index.html
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