The phrase "a certain third" is correct and usable in written English.
It can be used when referring to a specific third party or element that is not explicitly named or identified.
Example: "In the discussion, a certain third was mentioned, but their identity remained a mystery."
Alternatives: "a specific third" or "an unnamed third".
Another, this one more plausible, involved the desire to see a singular event, a home run slugged by a certain third baseman, before the Yankees skipped town for a more meaningful series against Tampa Bay.
After an exhausting first period inventing elaborate ways of miming household chores, I slip into the hubbub of the staff room, where a hushed discussion is taking place about what to do with a certain third year pupil.
This formula states that "if one proposition implies a second one, and a certain third proposition is true, then if either that third proposition is false or the first is true, the second is true".
The two Chelsea players combined again for what looked to be a certain third goal in the dying minutes, but the Swindon keeper produced a fine stop once again before it was scrambled away.
"In Search of Excellence" was one, "Good to Great" a second, and "The Tipping Point" a certain third.
He said friends who visit joke that the junks bring a certain "Third World charm" to the island.
Well-known episodes — the trip to China, the Pentagon Papers, Vietnam, the wedding of Nixon's daughter Tricia, and of course the fallout from a certain third-rate Washington burglary — take on a strange new coloring, revealing a curiously touching human dimension.
"We saw him as a certain first-rounder.
If cricket had one, Dravid, 39, would be a certain first-ballot Hall of Famer.
South Carolina was a certain sixth pick until its late-season slump.
By using this approximation the autocovariance and spectral density function for a certain first order system are obtained.
