Mbore
No chance, forget it — the flat Paraguayan refusal that closes a subject instead of answering it.
Related lesson: Paraguayan Spanish: A Survival Guide.
Hear it in context
—¿Me prestás tu auto? —Mbore.
'Will you lend me your car?' 'Not a chance.'
¡Mbore! Eso no fue así, yo estaba ahí.
No way! That's not how it happened — I was there.
Le pedí que venga y me dijo mbore nomás.
I asked him to come and he just flat out refused.
What It Actually Means
Mbore is an emphatic negative interjection: no, never, absolutely not, don’t be ridiculous. It is heavier than no and blunter than ni loco — the difference is that no answers a question while mbore dismisses it. Depending on what it lands on it reads as refusal (“I won’t”), denial (“that’s false”) or disbelief (“you’re joking”).
Where It Comes From
Guaraní, and beyond that the honest answer is that nobody agrees. It is listed in dictionaries of Paraguayan usage simply as an interjection of denial, and the folk explanations you will hear — a contraction of mba’e (“thing”, “what”), or a euphemism for something obscene — are guesses rather than documented derivations. Treat anyone who gives you a confident etymology with the same scepticism the word itself expresses.
How Natives Use It
Spoken, informal, and usually alone: a single word, falling tone, subject closed. It stacks happily with the national softener nomás (mbore nomás) and with nde when the refusal comes with an accusation. Paraguayans of every age and class use it; it is regional, not class-marked.
Common Pitfall
It is not rude in the way a swear word is rude, but it is brusque — a mbore to your boss’s request will be understood perfectly and not forgiven quickly. If you want a plain, neutral no in Guaraní, that word is nahániri. And keep it inside Paraguay: across the border in Argentina or Brazil, mbore buys you a blank look.