Superlative form of narrow: most narrow.(adjective)
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Use "narrowest" in a sentence
"Millay's house aka the narrowest house in NYC aka I'd love to live there"
"But in Ireland, which was Catholic and Nonconformist, landed property signified Episcopalian landed property, that is, the narrowest form of ascendancy."
"I confess that it is necessary to keep within certain limits, and that the narrowest are the best; also it must be allowed me that to be too scrupulous would spoil all."