al-Nudhūr is interpreted in three ways:
1. al-Nudhūr is used in the sense of warning; as in the following verses:
Warn the people (that is, warn the disbelievers of Mecca with punishment). (Yūnus 10:2)
It is the same for them whether you warn them (that is, whether you warn them!) or do not warn them (that is, do not warn them); they will not believe. (al-Baqara 2:6)
So that you may warn a people whose forefathers were warned (that is, just as their forefathers were warned), but they are heedless—so that you may warn a people, as their forefathers were warned, with the threats in the Noble Qur'an. (Yā Sīn 36:6)
It is the same for them whether you warn them (that is, whether you warn them) or do not warn them (that is, do not warn them); they will not believe. (Yā Sīn 36:10)
2. al-Nudhūr is used in the sense of news; as in the following verses:
This too is a warning (nadhīr) from the former warnings (that is, from the news of previous communities).
So that when they return to their people, they may warn them (that is, inform their people). (al-Tawba 9:122)
3. With the word al-Nudhūr, the messengers (rusul) are meant; as in the following verses:
Thamūd denied the warners (that is, the messengers). (al-Qamar 54:23)
The people of Lūt denied the warners (that is, the messengers). (al-Qamar 54:33)
And indeed, to the people of Pharaoh, too, the warners (that is, the messengers) came. (al-Qamar 54:41)
...Did there not come to you a warner (that is, a messenger)? They replied: "Yes, a warner (that is, a messenger) did come to us." (al-Mulk 67:8-9)
You are only a warner (that is, a messenger). (Hūd 11:12)