Final answer:
Maya priests regarded the movements of Venus as a powerful portent, meaning a sign of something about to happen.
Step-by-step explanation:
In the sentence provided, portent means a sign of something about to happen. It refers to something that is seen as a significant or meaningful indication of a future event. In the context of the sentence, the movements of Venus were considered by Maya priests to be a powerful sign, suggesting that they closely observed those movements for any potential significance.