What is the meaning of the Arabic term "millah"?

In a Nutshell: Millah linguistically refers to something that has been dictated or written. In the Islamic usage it is used to refer to foundational principles common to all shariahs (when used in a restricted manner), or to the deen Allah revealed (when used more broadly). The Linguistic Meaning Of Millah The term millah (ملة) is driven from the root malla (ملّ) which according to the famous classical Arabic dictionary Lisan al-Arab means "to dictate" giving the meaning of a given instruction. The dictionary al-Mu'jam al-Wasitt says it is also used to refer to principles of certain religions such as Judaism, Christianity and even polytheism. Islamic Usage The Qur'an used the term millah 13 times by two broad meanings. 1. Revealed or fabricated deen Allah says: إِنِّي تَرَكْتُ مِلَّةَ قَوْمٍ لَا يُؤْمِنُونَ بِاللَّهِ وَهُمْ بِالْآخِرَةِ هُمْ كَافِرُونَ "Indeed, I have left the millah of a people who do not believe in Allah, and they, in the Hereafter, are disbelievers." (Qur'an 12:37) وَلَنْ تَرْضَىٰ عَنْكَ الْيَهُودُ وَلَا النَّصَارَىٰ حَتَّىٰ تَتَّبِعَ مِلَّتَهُمْ "And never will the Jews or the Christians approve of you until you follow their millah." (Quran 2:120) مَا سَمِعْنَا بِهَٰذَا فِي الْمِلَّةِ الْآخِرَةِ "We (Quraysh) have not heard of this in the latest millah (Christianity as understood by ibn Abbas)." (Qur'an 38:7) The Prophet (saw) said: لاَ يَتَوَارَثُ أَهْلُ مِلَّتَيْنِ "People of two different millahs do not inherit from one another." (Ibn Majah, Vol. 4, Book 23, Hadith 2731) The above verses speak about corrupted religions that were originally divine (Judaism and Christianity) and fabricated religions such as polytheism. There are many other references to the same meaning as in Qur'an 7:88-86, 14:13, 18:20. The hadith also refers to inheritance of different religions' members of each other, such rulings are elaborated further in the juristic analysis and other dala'il (related references). (Ibn Ashur, At-Tahrir, Vol. 1, p. 2411) 2. Preserved shari'ah of Allah There are many verses that refer to the following of the millah of Prophet Ibrahim (as). I will only include one of them: قُلْ صَدَقَ اللَّهُ فَاتَّبِعُوا مِلَّةَ إِبْرَاهِيمَ حَنِيفًا "Say, 'Allah has told the truth. So follow the religion of Abraham, inclining toward truth …'" (Qur'an 3:95) The Qur'an narrates that Prophet Yusuf (as) said: وَاتَّبَعْتُ مِلَّةَ آبَائِي إِبْرَاهِيمَ وَإِسْحَاقَ وَيَعْقُوبَ "And I have followed the millah (shari'ah) of my fathers, Abraham, Isaac and Jacob." (Qur'an 12:38) In these verses, the term millah is used to refer to the revealed sharia. The term millah is used to refer either to a revealed shari'ah (or its principles) of Allah or corrupted or fabricated religions. Juristic Analysis Whilst millah is used to refer to certain religions or entities, the term deen is a more general and wider. Millah refers more specifically to shari'ah sent by God to guide the people and the principles (usul) of a religion. (Tafsir al-Biqa'i, Vol. 4, p. 322, ibn al-Athir, an-Nihayah, Vol. 4, p. 360) Asfahani (d. 502 A.H.) said: المِلَّة كَالدِينِ، وهُوَ اسْمٌ لِمَا شَرَعَ اللّهُ تَعَالَى لِعِبَادِهِ عَلَى لِسَانِ الأَنْبِيَاءِ لِيَتَوَصَّلُوا بِهِ إلِى جِوَارِ اللّهِ، والفَرْقُ بَيْنَهًا وبَيْنَ الدِّينِ أنَّ المِلَّةَ لا تُضَافُ إَلَّا إِلَى النَّبِيّ عَليه الصلاة والسلام الذِي تُسْنَدٌ إِلَيْهِ ... ولا تَكَادُ تُوَّجَدُ مُضَافَةً إلَى اللّهِ، ولَا إِلَى آَحَادِ أُمَّةِ النَّبِيّ صلَّى اللّهُ عَلَيْهِ وسَلَمَ، وَلَا تًسْتَعْمَل إلَّا فِي جُمْلَةَ الشَّرَائِعِ دُونَ آَحَادِهَا. "The term millah is similar to the word deen, referring to what Allah has legislated to His servants via the Prophets (saw) to reach paradise..." (al-Mufradat fi Ghara'ib al-Qur'an, Vol. 1, p. 471) Ghazali, however, argued millah refers to the foundational principles of revelation, common to all shariahs, saying: ِوالمِلَةُ عِبَارَةٌ عَنْ أَصْلِ الدِينِ والتَوْحِيدِ والتَقْدِيسِ الّذَيِ تَتَفِقُ فِيهِ جَمِيعَ الشَرَائِع "Millah is the principles ('usul) of deen, monotheism (tawhid) and canonization that all the other shari'ahs agreed on." (al-Mustasfa, Vol. 256) Marudi said: والفَرْقُ بَيْنَ المِلَّةَ والدِينِ أنَّ المِلَّةَ مَا شَرَعَهُ اللهُ، والدِّينُ ما اعْتَقَدَهُ النَاسُ تَقَرُّبًا إلَى اللهِ، فَصَارَ كُلَ دِينٍ مِلََةٌ، وليْسَ كلَ مِلَةٍ دِين "The difference between millah and deen is: millah is what Allah legislated, but deen is what people believed in as a kind of servitude to Allah. Thus every deen is considered millah, but every millah is not considered deen" (Tafsir al-Marudi, Vol. 2, p. 239) Qurtubi holds a similar view in his tafsir (Tafsir Qurtubi, Vol. 2, p. 91) Conclusion Millah refers either to deen (in a reduced meaning) or to the divine shari'ah that was revealed by Allah to guide nations. It also refers to the principle beliefs upon which the deen is established. References al-Asfhanahi, al-Mufradat fi Ghara'ib al-Qur'an Marudi, Tafsir al-Marudi Ghazali, al-Mustasfa