A person or thing that causes disgust or revulsion in others.
From 'disgust' plus the agent suffix '-er', which creates nouns meaning 'one who does X' or 'that which does X'. This productive suffix has been used in English for over a thousand years.
The '-er' suffix is so powerful in English that we can make an agent noun from almost any verb—'disguster' is rare because we don't usually need a word for something that disgusts, but the grammar makes it instantly understandable.
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