• Webster's Revised Unabridged Dictionary
    • a Insubmergible Not capable of being submerged; buoyant.
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Century Dictionary and Cyclopedia
    • insubmergible Incapable of being submerged.
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In literature:

Such are the insubmergable mirages of the soul!
"The Man Who Laughs" by Victor Hugo
That the lifeboat is insubmergible has been proved to some extent by the foregoing incident.
"Man on the Ocean" by R.M. Ballantyne
The splendid craft which he commanded was one of the self-righting, insubmergible boats of the Institution.
"Personal Reminiscences in Book Making" by R.M. Ballantyne
There is also a curious application of cork in the manufacture of a fabric that renders those who are clothed with it insubmergible.
"Cork: Its Origin and Industrial Uses" by Gilbert E. Stecher