I remembered also the necessity imposed upon me of either journeying to England or entering into a long correspondence with those philosophers of that country whose knowledge and discoveries were of indispensable use to me in my present undertaking.
There are no more uses of "indispensable" in the book.
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Then a big pot was brought out as we raced to retrieve our indispensable spoons and bowls.
Leon Leyson -- The Boy on the Wooden Box
In fourteen years in Bluffton he had sired two sons and managed to worm his way so completely into Bennington’s life and make himself so indispensable that he sometimes seemed like Bennington’s third leg.