A nebbish is an ineffectual person, someone timid, submissive, weak, helpless or hapless, a nonentity. He's unlucky, but mainly because he’s a loser right through to the core.
It’s an adjective formed from
one of the most characteristic of Yiddish words. It was originally "nebech". In Yiddish it was originally an
interjection, roughly meaning “You poor thing!”. Americans had trouble saying this word when it first appeared in the
English language at the end of the nineteenth century, and they changed it to nebbish, with nebbishy as the much less common adjective.
Sarah: "He just sits there, and every time I make a
suggestion, he goes with it, but mostly because he doesn't
understand what I'm saying and has no dang
opinion for himself!"
Marie: "Gosh, he's so nebbish."