a long shot
1. A bet that has a low probability of winning. That horse is a long shot, but the bet will pay well if he wins the race.
2. Something that has a very small chance of succeeding. I know it's a long shot because of his busy schedule, but maybe I can convince him to help me with this project. Her candidacy was a long shot from the beginning, and her landslide defeat was no surprise.
a long shot
1. If you describe a way of solving a problem as a long shot, you mean that there is little chance that it will succeed, but you think it is worth trying. You could try to find her. It's a long shot but you could start with the phone book.
2. You can also say that something is a long shot when it is very unlikely to happen. It seemed such a long shot, me walking over the hills, and seeing you at the end of it. Compare with by a long shot. Note: The reference here is to someone shooting at a target from a very long distance.
a ˈlong shot(informal) an attempt or a guess which you do not expect to be successful but which is worth trying: Try ringing him at home. It’s a long shot, I know, but he might just be there. ♢ ‘Are you going to apply for the manager’s job?’ ‘I don’t know. It’s a bit of a long shot, isn’t it?’A long shot is a shot fired from a long distance and so unlikely to hit its target.
long shot, (not by) a
(Not) a remote chance. Early firearms were notoriously inaccurate, and a shot from a distance rarely hit the target. In the late eighteenth and early nineteenth centuries a long shot meant just that, a shot fired from afar. By the late nineteenth century the term had been transferred to other improbable circumstances, such as a wild guess or, more specifically, a bet against considerable odds. From about 1865, however, it also meant far-fetched, as in this OED citation from Young Gentleman’s Magazine (1873): “This did not, however, suit her long-shot tactics.”
See also: long