means A cold-blooded, scaly vertebrate — like a snake, lizard, turtle, or crocodile — that regulates its body heat from the outside world rather than burning its own fuel.

from From Latin 'reptilis,' meaning 'creeping,' from the verb 'repere,' 'to crawl.' The word slithered into English through Old French in the medieval period, carrying its literal sense: a thing that moves low to the ground, belly to the earth. That crawling image stuck so hard that 'reptile' became an insult long before it was a tidy biological class — to call someone a reptile was to call them a groveling, low creature. The scientific pigeonholing came later.