submerge

To submerge is to push or sink fully under water. Submerge the jar, submerged rocks, fully submerged.

Fully is the point — a partly covered thing is not submerged — which matters in cooking, in navigation and in law, where submerged land is a distinct category. Figuratively, to be submerged in work is to be under it entirely. Note that the Latin is sub plus mergere, to plunge, the same root as emerge and merge.