to smear or daub thickly with a substance, or to slobber and smear.
From be- (prefix) + slubber (possibly from Low German slubdern or related to slumber). The word combines the idea of messy coating with intensive action.
Slubber is related to slumber in some theories—both involve a kind of 'heaviness' or 'muddiness'—but honestly the etymology is murky, which is funny because the word describes something slimy and unclear!
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