Archaic. Often interchanged for 'dragon' although the connotations are radically different.
People think of dragons as grand, fierce, mystical, majestic creatures. You say 'dragon' and there is an awe inherent in the word.
This impression is not correct, for 'wyrm'. Wyrm is the more archaic version, both in language and in meaning. A *wyrm* is definitely a reptilian beast, in form dragon-like, but there the resemblance stops. Dragons are fire's creatures. A wyrm, if one were to involve elemental theory, is really more of an earth creature. Like the oriental dragons are water's creatures, the wyrm is of a more earthy nature. Yes, some are fire breathing, some are winged (really making them elemental spirits, interchangeable... all elements connect... but I digress...) but they are of an earth-mind.
They are lanky creatures and prefer to be protected by their scales and their hiding, than to fight. Creeping, misunderstood creatures they are, hiding and lurking. They are not 'of this earth' but of something older, something ancient perhaps older than time itself. There is an innate *nobility* and an AMAZING *wisdom* that comes from years and years... but they are misunderstood, hunted and destroyed when all they want is to be left alone to *exist* peacefully, hidden away.