Is 'contemporary' ambiguous and if so is there a better word?
It's not that I don't know what contemporary means.
It's just that in my specific sentence (below) I'm not sure if it could be ambiguous. If it is ambiguous, then I'm looking for a word or phrase to substitute for 'contemporary' that makes it clear that the pagan philosophers lived at a time when Christianity was still in its infancy. Here's the sentence:
And that’s what the early modern readers of Celsus, Porphyry and Julian were bent on discovering: how early Christianity was perceived and judged by contemporary pagan philosophers.
'Contemporary' is meant to refer to the pagans of antiquity, not of the early modern period (and certainly not modern-day pagans). Is this clear? Would 'coeval' make it any clearer?
And that’s what the early modern readers of Celsus, Porphyry and Julian were bent on discovering: how early Christianity was perceived and judged by coeval pagan philosophers.
Or do I have to completely changed the sentence to be unambiguous:
And that’s what the early modern readers of Celsus, Porphyry and Julian were bent on discovering: how early Christianity was perceived and judged by the pagan philosophers who witnessed its birth and infancy.
(I would prefer not to have to use the last sentence, since my sentence is a translation from German and I would prefer to stay more closely to the original text.)
I think usage of contemporary would be less ambiguous if you reworded slightly:
...how early Christianity was perceived and judged by its pagan philosopher contemporaries.
This way, you're explicitly stating that the pagan philosophers are contemporary to early Christianity.
Also, if you wanted, you could remove reference to specific pagan philosophers:
...how early Christianity was perceived and judged by contemporary [or contemporaneous] pagan philosophy.
And that’s what the early modern readers of Celsus, Porphyry and Julian were bent on discovering: how early Christianity was perceived and judged by contemporary pagan philosophers.
As I read that sentence, the words "was perceived" make it clear that the question is not about the perception of those "who are living and writing today" (as suggested in another answer). Additionally, the statement "that's what the early modern readers of ... were bent on discovering" makes it abundantly clear that the time period referred to cannot be later than the "early modern period".
One alternative version would be:
And that’s what the early modern readers of Celsus, Porphyry and Julian were bent on discovering: how early Christianity was perceived and judged by their contemporary pagan philosophers.
but to me, the word "their" then reads back to "the early modern readers".
But if you were to write:
And that’s what the early modern readers of Celsus, Porphyry and Julian were bent on discovering: how early Christianity was perceived and judged by its contemporary pagan philosophers.
then (to me) the only predecessor for "its" could be "early Christianity", thus making it clear that the reference to "contemporary pagan philosophers" refers to those contemporaneous with "early Christianity" (which is what I understand the reference in your question to "the pagans of antiquity" to mean).
(P.S. I should point out that I started writing this answer before the answer by Acccumulation had appeared.)