Superlative form meaning most characterized by gutters, channels, drop-like markings, or guts/courage.
From 'gutty' or 'gutte' + superlative suffix '-est', indicating the highest degree of having grooved quality or (separately) the most courageous.
In Victorian slang, 'gutty' also meant courageous, so 'guttiest' could describe either the most drop-spotted surface or the bravest person—English's delightful homonyms!
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