A name for the race of Dragons, and especially those wingless kinds (such as Glaurung himself) who crawled on the ground.
Notes
1
The Old English wyrm itself seems to descend from an Old Norse word, ormr, meaning 'serpent'. The Greek word drakon means 'serpent', too, so that if we follow the history of the words back far enough, 'worm' and 'dragon' both mean exactly the same thing.