A thick, sticky, messy substance or liquid; also used informally to describe something of poor quality.
American slang from the mid-20th century, possibly from the onomatopoeia of thick liquid sounds, though some suggest it's related to 'gallop' or 'gloop.'
The word 'glop' and its cousins like 'gloop' and 'goo' are among English's most satisfying onomatopoeia—they sound exactly like the gross, sticky substances they describe.
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