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Webster 1913 Edition

Adj.

[L.

innavigabilis

: cf. F.

innavigable

. See

not, and

Incapable of being navigated; impassable by ships or vessels.

Drygen.

–

In-nav′i-ga-bly

adv.

Adj.

[L. innavigabilis; in and navigabilis. See Navigate.] That cannot be navigated; impassable by ships or vessels.

innavigable ‎(comparative more innavigable, superlative most innavigable)

Incapable of being navigated; impassable by ships etc.
(Can we find and add a quotation of Dryden to this entry?)