The phrase "a singular accomplishment" is correct and usable in written English.
You can use it to emphasize a unique or noteworthy achievement.
Example: "Winning the Nobel Prize was a singular accomplishment that changed the course of her career."
Alternatives: "a remarkable achievement" or "a unique success."
Just a few decades ago, this would hardly have been a singular accomplishment.
What the space programs of the world achieved at Baikonur yesterday is a singular accomplishment.
That's good for Apple, and for its mission to mark the iPhone as a singular accomplishment of technology and design.
In the regimented club scene, a casteless society, à la the disco equalizer Studio 54, is a singular accomplishment.
N.C.A.A. President Mark Emmert called it a singular accomplishment to make changes that "set a completely new tone" for the rules.
Because of his fixation on white-collar crime, in these campaign appearances Morgenthau neglects a subject that most district attorneys would embrace as a singular accomplishment: violent crime in Manhattan has plummeted in the past thirty years.
Only Obama's most vicious critics deny him the singular accomplishment that, in a way, he shares with the country as a whole: he's the first black president.
Just as he had nothing to point to and no accomplishments as a Senator, Obama has not delivered one singular accomplishment as President.
They said Dr. Khan's singular accomplishment of helping give Pakistan a nuclear deterrent against India eclipsed his wrongdoing.
Mr. Trump's singular accomplishment was showing the world he is a publicity hound with no credibility.
The newspaper headlines here daily scream of scandal, beginning at the very top with President Jacob Zuma, whose singular accomplishment has been to make Mbeki look like a paragon of virtue.
