Drunk or intoxicated; or to move with a splashing sound through water or liquid.
Possibly from Scandinavian 'slusk' or imitative origin, similar to 'slush.' As a verb it means to move liquid around noisily.
The onomatopoeia of 'sloshed' is perfect—the actual sound of alcohol sloshing in a bottle matches the slurred speech of someone drunk, so the word mimics both the physical sound and the state of mind.
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