look up any word, like blumpkin:
 
1.
The act of flubbing lyrics or not keeping time with a band during a song
We had to keep practicing the song over and over because the singer welshed it.
by log the drummer May 08, 2011
 
2.
To cover, spray, smear or shart your own human feces within the confines of a house, room or dwelling.

(Past-Tense only)
*walks into a room covered in human feces*

Woah dude somebody totally welshed in here!
by fubfub October 20, 2010