Doom: an unpleasant or disastrous destiny; "everyone was aware of the approaching doom but was helpless to avoid it"; "that's unfortunate but it isn't the end of the world" (source:
Google)
Cornucopia: also known in English as the Horn of Plenty, is a symbol of prosperity and affluence, dating back to the 5th century BC; a symbol of plentitude, strong harvests and abundance. (source:
Google)
That said, the words 'Doomer' or 'Cornucopian' in the context of peakoil, can vary widely and it really depends on the perception of 'Person A' who would be listening to 'Person B' describe the effects of peakoil (or any other topic that could have global ramifications, like Global Warming). For an analogy, in the investing world the person having the relatively negative outlook is the 'Bear', versus the relatively positive outlook of the 'Bull' (see CNBC). So Bull is to Cornucopian as Bear is to Doomer.
Now for a specific definition of both in the context of peakoil.com, I, for example, would be considered a doomer and KingM, for example, would be a cornucopian.
But we all go through phases and that's why it's mostly about perception.
"If you are a real seeker after truth, it's necessary that at least once in your life you doubt all things as far as possible"-Rene Descartes
"When you have excluded the impossible, whatever remains however improbable must be the truth"-Sherlock Holmes