Pronunciation: (sem"ē-sub-mûr'su-bul, sem"ī-),[key] —n. Also called sem'isubmers'ible rig'. a self-propelled barge that is mounted on partially submerged legs supported by underwater pontoons, rides at anchor, and serves as a work base and living quarters in deep offshore drilling operations.
—adj. of, for, or pertaining to a semisubmersible.