DeLillo's meshuggener

I struggle on (gently), with Don DeLillo's Underworld. It's a novel rendered at least triply nostalgic in light of recent events (not only with respect to (the archetype of) 'baseball' - the cover also sports an image of the twin towers engulfed in smog, and the silhouette of a lonely...is it a bird?) Nostalgia...is this the word? A bit weary of these archetypes all the time, I admit. But for all its pretenses of layering and distances removed, perhaps DeLillo's prose is simply not abstract enough. Perhaps DeLillo, as far as writers of fiction go, is a bit sloppy and pretentious. It doesn't stop me entirely from feeling a sort of communion with the suffering figure of John Edgar Hoover (that is, a communion with his inability to feel a communion). Anyway, I liked this passage:

And the crowd is also in this lost space, the crowd made over in that one-thousandth of a second when the bat and the baseball are in contact. A rustle of murmurs and curses, people breathing soft moans, their faces changing as the play unrolls across the grassy scan. John Edgar Hoover stands among them. He is watching from the wide aisle at the head of the ramp. He has told Rafferty he will remain at the game. No purpose served by his leaving. The White House will make the announcement in less than an hour. Edgar hates Harry Truman, he would like to see him writhing on a parquet floor, felled by chest pains, but he can hardly fault the President's timing. By announcing first, we prevent the Soviets from putting their own sweet spin on the event. And we ease public anxiety to some degree. People will understand that we've maintained control of the news if not of the bomb. This is no small subject of concern. Edgar looks at the faces around him, open and hopeful. He wants to feel a compatriot's nearness and affinity. All these people formed by language and climate and popular songs and breakfast foods and the jokes they tell and the cars they drive have never had anything in common so much as this, that they are sitting in the furrow of destruction. He tries to feel a belonging, an opening of his old stop-cocked soul. But there is some bitter condition he has never been able to name and when he encounters a threat from outside, from the moral wane that is everywhere in effect, he finds it is a balance to this state, a restoring force. His ulcer kicks up of course. But there is that side of him, that part of him that depends on the strength of the enemy.
Look at the man in the bleachers who's pacing the aisles, a neighborhood crazy, he waves his arms and mumbles, short, chunky, bushy-haired - could be one of the Ritz brothers or a lost member of the Three Stooges, the Fourth Stooge, called Flippo or Dummy or Shaky or Jakey, and he's distracting the people nearby, they're yelling at him to siddown, goway, meshuggener, and he paces and worries, he shakes his head and moans as if he knows something's coming, or came, or went - he's receptive to things that escape the shrewdest fan.

My important question is, what the hell is a "meshuggener?"