I know Daf Yomi has already started the second perek, but I have another two posts in me on the first word of the masechta, so I'm sticking with daf 2a and thereabouts for a bit longer.
First, a summary of posts so far on this topic.
The first Mishna begins אור לארבעה עשר בודקין את החמץ לאור הנר. Based on Rashi's comment that this is the correct girsa, we know that there are other variants in existence. In this post I discuss some of the possibilities. The most likely is JTS's manuscript which has אור ארבעה עשר, which parallels the phraseology in the third Mishna. Another possibility is that of Rabbenu Chananel, which has אור ל)ארבעה עשר בודקין את החמץ לאור הנר), with אור ל in parentheses and thus perhaps not present.
The gemara begins:
מאי אור רב הונא אמר נגהי ורב יהודה אמר לילי קא סלקא דעתך דמאן דאמר נגהי נגהי ממש ומאן דאמר לילי לילי ממש
Rashi dislikes the end portion, ומאן דאמר לילי לילי ממש, since of course we would think that leilei, night, means actual night, and in fact that is how we conclude! He proposes emending the text to eliminate this last phrase. In this post, I examine various manuscripts and note that the JTS manuscript omits the word ממש in reference to both naghei and leilei and instead writes:
דמאן דאמר נוגהי צפרא
"that the one who says noghei means morning (tzafra)"
ומאן דאמר לילי אורתא
"and the one who says leilei means evening (`oreta)"
which I believe Rashi would not be so compelled to emend out of existence.
How does אור, which means "light," come to mean "night?" In this post, I discuss how the Hebrew word `or, and its Aramaic cognate which the gemara uses to define it, `oreta, can mean "night." Jastrow gives the basic meaning of the word as break, perforate, and tries to prove this from pesukim and gemaras. Thus, `or can mean break of day, break of night, twilight, etc.. Hasagot haRaavad suggests it is the early part of night when it is still night, and the Ran suggests that the positive word `or is deliberately chosen here because it is the beginning of a masechta.
The gemara concludes that both Rav Huna and Rav Yehuda intend to render the `or of our Mishna as "night." The difference in their formulation is merely a result of different regional dialects. I point out in this post that there could be more to it than that, for Rav Yehuda uses the same formulation as the academy of Shmuel as Nehardea, and Rav Yehuda studied under Shmuel. Perhaps he could be using the exact language as his Rebbe, as we have seen Tannaim and Amoriam take care to do in other instances.
Is the distinction really one of regional dialect? Perhaps the gemara is covering up a real difference in opinion, and naghei must mean light, and thus daytime. In this post, I point out that Abaye uses the word naghei to mean night, and so it is absolutely true that naghei means night and was intended by Rav Huna to mean night. In the same post, I also point out that we know a bit about the biographies and histories of many of those mentioned in the gemara, such that when the gemara states that each one (Rav Huna and Rav Yehuda) is talking in his local dialect, we know where each of these lived. Rav Huna, who says naghei, was the head of the yeshiva at Sura after the death of Rav, and Rav Yehuda, who says leilei, founded the yeshiva at Pumpedita after Nehardea, the academy of Shmuel, was destroyed. However, I point out that Abaye, a leader head of the yeshiva at Pumpedita, does not use leilei, but rather naghei, in seeming contradiction to the gemara's statement. Finally, the academy of Shmuel, at Nehardea, used leilei. I suggested that the gemara intends the loval dialect where they grew up, not where they eventually led the yeshiva, or alternatively, the dialect of both Sura and Pumpedita was naghei, but Rav Yehuda is using the language of Nehardea, for he studied under Shmuel (though he also studied under Rav).