A patient's grammar, sentence structure, and comprehension are all entirely intact, but she has a specific, isolated difficulty finding the names of objects when asked, sometimes substituting a vague description in place of the correct word. Before revealing the answer: is this central aphasia?

No, this is more consistent with nominal aphasia than central aphasia. Central aphasia differs from nominal aphasia in that grammar and syntax, not just word-finding, are disturbed, whereas here grammar and comprehension are both entirely intact, with the disturbance isolated specifically to naming, which is the defining pattern of nominal aphasia rather than the broader, combined disturbance seen in central aphasia.