Incapable of being navigated; impassable by ships etc.(adjective)
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Use "innavigable" in a sentence
"Master Thorne, in the sixteenth century, expressed the resolute spirit of that energy in a phrase: "There is no land uninhabitable, nor sea innavigable"; and in every part of the globe this British spirit has applied itself to many a land that looked hopeless at first, and has frequently found it to be one:"
"Nothing showed under the innavigable depths of Sara's eyes."
"A month since the Elbe was cleared of ice, and now, contrary to the expectation of all, the cold had returned to such a degree, that it was a second time innavigable."