unsubmersibleadj.
Etymology: Previous versions of the OED give the stress as: unsubˈmersible.
the world > matter > properties of materials > lightness > [adjective] > rising due to lightness > buoyant
1891 W. K. Brooks 58 Two beautiful unsubmersible claires [= oyster-tanks].
This entry has not yet been fully updated (first published 1926; most recently modified version published online June 2019).