mersnakeEtymologyFrom mer- + snake. Compare Middle English mereneddre (“sea-snake, lamprey”), from Old English merenǣddra, merenǣddre, merenǣdre (“lamprey, sea snake”, literally “sea-adder”).nounA sea snake.“I asked casually while we walked past a few buildings with split columns painted with a pit of mersnakes eating raw flesh.”A mermaid snake.