Wow. That's a good question. I've never come across that before.
Here's the verse:
43. And the king (of Egypt) said: "Verily, I saw (in a dream) seven fat cows, whom seven lean ones were devouring - and of seven green ears of corn, and (seven) others dry. O notables! Explain to me my dream, if it be that you can interpret dreams."
The word is
sunbulatin. According to my dictionary, the word just means "ear" or "spike".
Also, keeping in mind what you said, the muslims at the time of the Prophet saws wouldn't have understood the verse as corn anyway! They didn't have corn. So their understanding would have been some kind of grain as you suggested.
Hope this helps.

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