the.com/sea turtle

means A large marine reptile with a streamlined shell and paddle-like flippers that spends almost its entire life swimming the ocean, returning to land only to nest.

from Straightforward English compound: 'sea' plus 'turtle.' 'Turtle' itself likely comes from the French 'tortue' (tortoise), which English sailors reshaped — possibly influenced by 'turtle' the dove-word (from Latin 'turtur') — into the form we use today. No deep mystery here, just centuries of sailors and naturalists needing a plain word for the shelled things swimming alongside their ships.