"The opposite of being drunk, its as sober as you can ever be. It strips away all the illusion, all the comforting pink fog in which people normally spend their lives, and lets them see and think clearly for the first time ever. Then, after they've screamed a bit, they make sure they never get knurd again" - Terry Pratchett
A hug (or cuddle). The original Dutch word 'knuffel' was deemed to be English sounding enough to be fully incorporated. Knuffle sounds the same and means the same.
The opposite of drunk. If you are drunk you are unable to perceive reality properly, being knurd is having your comfortable illusions of life being stripped away and all of life's terrors are exposes.