Superlative form of 'greasy'; the most oily, slippery, or containing the most grease of a group.
From 'greasy' + '-est' (superlative suffix); following the same pattern as 'greasier,' the superlative form marks the highest degree of the quality.
The 'greasiest' spoon diner is a beloved American term for an unpretentious, no-frills restaurant where the food is hearty and the grills probably haven't been cleaned since breakfast—it's a mark of authenticity, not an insult, because those places serve real food.
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