The story
From Act I, scene ii, of The Tempest (1610–1611) by the English playwright William Shakespeare (1564–1616), spelling modernized: “Full fathom five thy father lies, / Of his bones are coral made: / Those are pearls that were his eyes, / Nothing of him that doth fade, / But doth suffer a sea-change / Into something rich and strange”. The passage refers to how a drowned man’s body lying on the sea bed had been transformed by the sea.
Etymology from Wiktionary, CC BY-SA 4.0.