A great Scots word, that. It sounds like what it is, and looks like the photo, taken yesterday on the old racecourse at Groenendaal, above the abbey ruins.
Scots sits within the North Sea Germanic world. The word is likely linked to Old Norse, particularly drjúgr, meaning enduring or long-lasting, with a possible echo of drjúpa, to drip slowly.
Over time, the sense seems to have settled into something more atmospheric. Not just wet, but persistently so.
The word exudes dampness.
Its usage also extended to sermons, apparently.