The phrase "an enmity" is correct and can be used in written English.
It refers to a state of deep mutual hatred or animosity between two individuals or groups. Example: The two neighboring countries have had an enmity lasting for decades, with frequent border clashes and diplomatic conflicts.
This has apparently fed an enmity between Tillerson and Haley.
Croatia's greatest rivalry is with Serbia, an enmity born before the break-up of Yugoslavia.
The debate, he said, has "an enmity that in my 37 years as a legislator I have never seen".
The brutal 19th-century conquest of the Caucasus created an enmity, wrote Tolstoy, "stronger than hatred, for [the Chechens] did not regard those Russian dogs as human beings".
That, perhaps, is because theirs is not an enmity rooted, particularly, in soccer: Napoli and Juventus have only fleetingly been peers on the field.
Their different backgrounds and personalities - Coe well-educated and charming, Ovett working-class and reserved - suggested an enmity between them which Coe said was not there.
Mr Soros, Mr Steinmetz's friends claim, has got it in for the diamond tycoon, due to an ancient enmity over a telecoms deal in years past.
Mr. Koppel interviews her father, Marc Klaas, identified as a "victims' advocate," who has an understandable enmity toward violent criminals.
There's an old enmity between Nazi-ish men in suits and a Holocaust survivor with a sword, a clash that leads to one of the bad guys announcing, "The Great Game is over, Jew".
"Now it's a symbol of enmity, a symbol of division, a symbol of all the bad things".
These incidents created an enduring enmity between the military establishment and APRA that would last for more than 50 years.
