A deep gully, ravine, or erosion valley, especially in South African or Southern African landscapes.
From Zulu/Bantu language 'idonga' (gully). The word entered English through contact with Southern African languages and describes the distinctive geographical feature common to that region.
This is a perfect example of how English borrowed words from Indigenous African languages when European settlers encountered landscapes they'd never seen before—dongas are such distinctive features that English just adopted the local name!
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