Superlative form of proper: most proper.(adjective)
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Use "properest" in a sentence
"Stain thy face, as I said, and grow thy beard, and thou'lt be the properest Sirkar's bargain in India!"
"Then he gave him last instructions as to the properest way of dealing with his neighbours and the due management of his affairs; after which he called to mind his brother and his home and his native land and wept over his separation from those he had first loved."
"It was the easiest way, and, beyond all comparison, the properest."