Question Summary:
Can i call a Christian ‘my master’?

Question Detail:

 
I want to ask about the permissibility of calling a Christian 'Sidi' (my master). In my country it's very common to say Sidi (the Indo/Pak equivalent is probably Bhai Sahab or Hazrat). We say this to all old people. It's taken from Sayiddi. I work with a Christian man, and sometimes by habit, I say to him Sidi.
What is the ruling of this/is it haram?
Also, I read on the following website (http://hidayaresearch.com/the-supplement-to-word-or-act-of-kufr/) in number 30 of things which cause disbelief to respect a disbeliever/kiss the hand of a priest causes disbelief, so would calling a Christian "Sidi" cause disbelief - I don't mean respecting his religion, just respect out of his old age, and it's really just a habit.

Answer :

In the Name of Allah, the Most Gracious, the Most Merciful.
As-salāmu ‘alaykum wa-rahmatullāhi wa-barakātuh. 
If it is a normal practice (urf) in your area to address an elderly person by the term sidi, then addressing to Christian person by sidi will not constitute kufr[1].
Abu Ali ad-Dagestani
Moscow, Russia
Checked and Approved by,
Mufti Ebrahim Desai