A feeling of what life would be like without one's wife, in this case personified by Opal Crankshaft, first used by Earl Pickles.
Earl: You know, Ed, I feel kind of Opal-Less.
Ed: What do you mean?
Earl: Well, that was my wife. Since you married her I miss her.
Ed: Well, without her I'd be Opal-Less myself.
Earl: Ed, I hope you never have to find out.