a blanket dampened with water so as to extinguish a fire.
a person or thing that dampens enthusiasm or enjoyment: Nobody asked him to join the group because he's such a wet blanket.
wet-blan•ketPronunciation: (wet'blang'kit), [key]
to extinguish (a fire) with a wet blanket.
to dampen the enthusiasm or enjoyment of (a person, group, etc.).
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.