I have a shirki (related to polytheism) nickname, Rabbi (my lord), which was given to me by my cousin in my childhood. My relatives and neighbours only call me with that name. Most of the people of our society are ignorant, they do not know about Tawheed (pure monotheism), Asma ul Husna (the Names of Allaah), and so on. They called my grandfather Rahman because his name was Abdur Rahman. Now, my question is: if they call me with that name and I respond to them, will I be a sinner or taghoot (rebel) then?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah and that Muhammad, sallallaahu ʻalayhi wa sallam, is His slave and Messenger. 

It is prohibited under Islamic law that people address each other as Rabb (Lord) so as to preserve the refined status of lordship for Allaah, The Exalted. Abu Hurayrah reported that the Prophet, sallallaahu ʻalayhi wa sallam, said, “Do not say, 'feed your lord (rabbak), help your lord in performing ablution, or give water to your lord,' but you should say instead, 'sayyidi' (my master; e.g. feed your master), or 'mawlaay' (my guardian). And do not say, 'my slave' (ʻabdi), or 'my female slave' (amati), but you should say instead 'my boy/lad' (fataay), 'my girl/lass' (fataati), and 'my servant' (ghulaami).” [Al-Bukhari and Muslim]

Al-Haafith Ibn Hajar wrote:

“His words, 'Do not say, 'Feed your lord...etc'' are only examples in this regard. These examples were specifically mentioned in the hadeeth because they were commonly used in people's interactions ... The hadeeth indicates the prohibition of calling one's master 'Rabbi' and for others to refer to his master as 'Rabbuk'. The reason for the prohibition is that the right of lordship belongs to Allaah alone because the lord is the possessor and sustainer, and that is true only of Allaah, The Exalted. Al-Khattaabi said, 'The reason for which it is not allowed (to call another person Rabbi) is that man is under the care of Ar-Rabb (the Lord, Allaah) and is required to show sincere belief in the Oneness of Allaah (Tawheed) and avoid associating anything with Him (shirk); so, it is disliked for him to use the same name lest it comes under the heading of shirk. There is no differentiation in this case between the free man and the slave. As for all animals and inanimate objects, which are not obliged to carry out acts of worship, it is not disliked to use this word in reference to them, such as saying Rabb Ad-Daar (owner of the house) or Rabb Ath-Thawb (owner of the garment).' Ibn Battaal said, 'It is not permissible to call anyone except Allaah, Rabb (lord), just as it is not permissible to call anyone else Ilaah (god). What is to be used exclusively for Allaah is the word Rabb (Lord) indifinitely without putting it in the possessive case. However, when it is used in the genitive case, it is it permissible to use it, such as when Allaah tells us that Yoosuf (Joseph) said, 'Mention me to your Lord' and 'Return to your Lord,' as is stated in the Quran [chapter 12, verse 50] and when the Prophet, sallallaahu ʻalayhi wa sallam, said, describing the portents of the Hour, 'When the slave woman gives birth to her lord (Rabbaha, i.e., her master).' This indicates that the prohibition on using this word applies only to its use indefinitely(i.e. without putting it in the possessive case), and it is possible that the prohibition is meant to indicate dislikeability; so the aforementioned texts are taken to mean permissibility. It is also said that the prohibition is exclusive to other than the Prophet and it does not contradict what is mentioned in the Quran; since what it is not allowed is to use the term repeatedly and take that usage as a habit, and it does not mean that it is forbidden in all cases.'” [Fat-h Al-Baari]

Ibn ʻUthaymeen was inclined to the view suggesting that the prohibition in the hadeeth is regarding using it repeatedly. He wrote, "Perhaps this is the most likely possible interpretation of the hadeeth that reads 'Do not say, 'Feed your lord, help your lord in performing ablution....; the prohibition in this context refers to repeatedly using the term Rabb in reference to one's master because these services are repeatedly carried out by the servant for his master. There is no doubt that the more it is feared that using such a term incurs sharee'ah violations, the more dislike of such an act is further emphasized and perhaps amounts to prohibition.”

Since most of your neighbors and relatives call you with this nickname (Rabbi), you should not answer anyone who calls you with it so as to deter them from doing so. Were they to know that you would not answer them if they called you with this nickname, they would be compelled to call you with your name instead. For more benefit, please refer to fatwa 271513.

Allaah knows best.