Wiktionary
by a long shot
prep.phr. (context idiomatic usually with a negative English) By a wide margin; indicates a very big difference or disparity.
WordNet
by a long shot
adv. by a great deal; "he is the best by a long shot"; "his labors haven't ended there--not by a long shot"
Usage examples of "by a long shot".
If the Tersae were behind it, he wouldn't be the only human, by a long shot, with a score to settle.
Except Ted and I weren't on a first-date basis anymore, not by a long shot.
Not the smartest by a long shot, but good enough to be in Planetary Integration.
All the eavesdropping, if you choose to call it that, was not done here, either, by a long shot, Worthington.
Cheers went up in the crowd and a new song started, some of the moment broken, but not all of it-not by a long shot.