a non-denial denial
A statement that seems and/or is intended to act as a direct denial to an allegation, but which, when taken literally or examined closely, does not deny the allegation at all. The phrase is most commonly associated with evasive answers of politicians facing scrutiny or accusations of misconduct. When pressed by journalists over certain large, undisclosed expenditures he had recently made, the senator gave a classic non-denial denial of any wrongdoing, stating ambiguously that any such spending was simply associated with the running of his campaign.
lex dubia non obligat
A Latin phrase that frees one from a contract or other legal obligation that is not morally sound. In English, the phrase means "a dubious law is not binding." As your lawyer, I think we should absolutely take them to court—the terms of this contract are unethical. Lex dubia non obligat!
non-starter
1. An issue, topic, or person that makes no progress or shows little evidence of future success. I know you worked really hard on that proposal, but it's a non-starter—the committee refuses to even consider it. You want to be a doctor? Boy, that's a non-starter—you can't even handle the sight of blood! I wouldn't have too much faith in Bobby—he's a nonstarter, and this business will probably just become another in a long line of failures for him.
2. sports One who does not start the game or race. This phrase is often used in horse racing. I watched the race—what happened to our horse? Why was he a non-starter? I may be a non-starter now, but my goal is to supplant the first-string quarterback in time.
non sequitur
A statement that does not logically fit into the current conversation. Good luck getting answers from him—his every response to my questions so far has been a non sequitur. A: "I changed the oil in the car." B: "Well, that's a complete non sequitur, since I asked if you were hungry!"
sine qua non
A necessary, essential, or required element. The Latin phrases translates literally to "without which not." Some consider a good education to be the sine qua non of a successful career.
a non sequitur
a statement which does not seem to be connected with what has just been said 'Have you arranged for us to visit Eileen?' I asked. 'But I thought you were coming by train', said Gwen, in what seemed a complete non sequitur.
persona non grata
(formal) someone who is not acceptable or not welcome He published a book criticizing the war and was instantly declared persona non grata by the authorities.
a sine qua non
(formal) something that is necessary, especially if you are going to achieve a particular thing (often + of ) The company sees training as the sine qua non of success.