The superlative form of 'fat,' meaning the most thick or plump, or the containing the most fat.
From Old English 'fætt,' meaning 'fatted' or 'fattened.' The superlative suffix '-est' was added to create the most extreme form, used since medieval times.
Interestingly, 'fat' as slang for 'excellent' reversed the word's negative association in some cultures—the 'fattest' beat or 'fattest' bass became a 1990s compliment, showing how context completely transforms meaning!
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