The true meaning of ‘Mawla’ within the context of Ghadeer Khumm is a topic of fierce debate. You find a number of Sunni scholars and individuals publishing refutations in books or online claiming that the word has well over a dozen meanings. They therefore state: ‘why would the Prophet ﷺ use a word that is so vast in meaning? After all, Mawla can even mean slave.’
To this we respond that anyone who uses such an argument is not being intellectually honest. When the Prophet ﷺ clearly states ‘Whomsoevers Mawla I am’ it obviously he does not mean slave, and the majority of the meanings of Mawla can automatically be discarded, leaving only a few main contenders. The two would either be Master/Authority over/More worthy over in authority, or possibly ally, or friend.
Unfortunately, you find articles published online which seek to try to put forward he idea that Mawla in its root means beloved, or indicates closeness. This is another dishonest attempt at misinterpreting the real meaning of the word and we will demonstrate this by consulting well respected Arab grammarians in the Sunni world.
1. In the famous Lisan Al-Arab dictionary  it states: he author of Lisan ul-Arab says: “Sibawayh says, “Wilaya stands for the guardianship of someone; taking charge of his “affairs and fulfilling his needs. The mawla (guardian) of a woman is he who undertakes the responsibility of contracting marriage on her behalf; she cannot get married without his agreement. Prophet Muhammad (PBUH) says: (For women who got married without the permission of their guardians, their marriage is invalid.) Thus, the real meaning of this word (mawla) is to take charge of a matter and to carry it out. The various uses of the expression simply express this basic fact, such as saying the word ‘man’ for Zayd, Amr and Bakr. Allah is called Mawla because He is the ruler of the affairs of Man.
2. Az-Zajjaj and al-Farra’ said, as mentioned in al-Fakhr ar-Razi’s book At-Tafsir  that “Mawla means worthier.” It was mentioned that Abul-Abbas al- Mubarrid had said that Mawla means worthier and most deserving..
3. Some senior scholars have discussed this subject in their books. Abu Ubayda says in his book Ghareebul-Qur’an : “Mawla means worthier.”
4. Abdul-Malik bin Marwan as his evidence: “Al-Anbari said in his book Tafsirul-Mushkil fil-Qur’an : “Mawla means the worthier.”
5. And Zamakshari, the famous Sunni scholar, combines both meaning in the following: “Az-Zamakhshari said in his Tafsir : “In fact, Mawla means your place, where it would be better for you to be. [a worthier place]“
6. Al-Halabi, in his book At-Taqrib , said: “Mawla, in fact, means worthier and the other expressions are derived from it. The master is a mawla because he is worthier to manage his slaves’ affairs and to bear with their faults. The slave is a mawla because he is worthier to obey his master. So too are the freed slave,the helper who is more worthy of helping whom he helps, the ally to be more worthy of supporting his allies, the neighbour to be more worthy of helping his neighbour and defending him, the son-in-law to be more worthy of his relatives, the imam to be more worthy of whom he leads and the cousin to be more worthy of helping his cousins.” Since the word (Mawla) means worthier, there is no excuse to turn it away from its real meaning and seek other ones.
We find that in the following tradition narrated in Musnad Ahmad  , Ali ibn Abi Talib himself interpreted ‘Mawla’ to mean master, and this tradition and its implications will be discussed in the very next section, and we highly recommend all readers to see what we have to say about it:
Rabah bin al-Harith said: ‘A group of men passed by Ali in Rahba and they said: ‘Peace be upon you our master (Maula). ‘He (Ali) said: how can I be your master (Maula) and you are Arab?’ They replied: ‘We heard Allah’s Apostle (pbuh) state on the day of Ghadir: ‘Of whomsoever I am his master (Maula) then this (Ali) is his master (Maula)’. Rabah said: ‘When they left, I followed them and asked (people): ‘Who are they?’ They answered: ‘They are group from Ansar and Abu Ayub al-Ansari is among them”. Shu’aib al-Arnaoot said: ‘The chain is Sahih’
Ali ibn Abi Talib عليهم السلام had been present in front of at least tens of thousands, if not an audience which neared the high five figures and would have clearly remembered Ghadir Khumm where he had been addressed as the Mawla over all of the believers. So it is worthy of note he immediately assumes the meaning of Mawla here means master and questions how he could be the Mawla if they were not slaves, but Arab (meaning free men). As we will discuss later on, this was an incredibly clever use of rhetoric by Ali ibn Abi Talib عليهم السلام to test the small group of Ansaar, among whom was Abu Ayub al-Ansari, who is respected as a righteous companion in Shia Islam. While we will discuss the full context and meaning of this tradition in a later segment, it suffices that we have demonstrated Ali ibn Abi Talib عليهم السلام understanding the meaning as master – something of great significance.
 Lisan Al-Arab.
 al-Fakhr ar-Razi At-Tafsir, vol. 29 p. 227, Egyptian edition.
 Abu Ubayda, Ghareebul-Qur’an.
 Al-Anbari , Tafsirul-Mushkil fil-Qur’an.
 Zamakshari, Tafsir, vol. 4 p. 66, Egyptian edition.
 Al-Halabi, At-Taqrib.
 Musnad Ahmad, Volume 38 page 54.