The superlative form of 'fruitful,' meaning the most productive, successful, or bearing the most fruit.
From 'fruit' plus '-ful' plus '-est' (superlative suffix). This archaic superlative competes with the modern 'most fruitful,' showing how English shifted from inflections to periphrasis.
Shakespeare and the King James Bible used 'fruitfullest' without hesitation, but by the Victorian era, writers were already preferring 'most fruitful.' This shift from '-est' to 'most' shows how English evolved to handle longer adjectives more smoothly.
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