Definition from Wiktionary, the free dictionary
nebbish (plural nebbishes)
- One who is fearful and timid, especially in making decisions and plans, in discussions, debates, arguments, and confrontations, and in taking responsibility.
- Actor Rick Moranis often plays a nebbish.
- (Can we verify(+) this sense?) (slang, mildly pejorative, US, chiefly New York) A loser.
- 2001, Foster Hirsh, Love, Sex, Death, and the Meaning of Life: The Films of Woody Allen 
- “I don't consider myself a nebbish,” Woody told interviewers early in his career, “but everyone else does.”
- 2001, Foster Hirsh, Love, Sex, Death, and the Meaning of Life: The Films of Woody Allen