According to this source: “The word anathema can be used as a regular noun (essentially meaning “a thing cursed”) and a determiner can appear in front of it, “an anathema.” However, it is usually used as what Burchfield calls a “pseudo-adjective” or a predicate nominative (no determiner): “The union was anathema to the middle management class.” Authority: The New Fowler’s Modern English Usage edited by R.W. Burchfield. Clarendon Press: Oxford, England. 1996. Used with the permission of Oxford University Press.”