In Japan, we call a person who is a senior in school, office, and social activity even a-year-ahead arriver “Senpai.” We address quite casually and lightly to a senior who entered school and office even a year ahead “Senpai!” in school, office, club and even on street.
The opposite of Senpai is ‘Kohai (後輩)’ literally meaning ‘late-coming (born) guy,’ but it is rare that the Senpai calls junior(s) ‘Kohai’ to his/her/their face(s). When we call somebody 'Senpai,' we don’t need to prefix Mr. / Ms, or even add the surname.
Though 'Senpai' can serve as a mentor to juniors and freshmen(women) in school, on sports, on profession in many cases, the nuance of the word would be just "Hey, my elder peer!" I understand Chinese have the same word / characters (先輩) besides "xiansheng (先生)" = Mr., literally meaning 'earlier-born'.
As I looked for the English counterpart of this word in Kenkyusha’s Readers Japanese -English Dictionary, it provided the following explanation:
Senpai – One’s senior. There is no English counterpart to this word because the relationship between senior and junior is not regarded as so important in English speaking countries. It would be more natural to say “He entered the company (university) five years before me,” if you wish to say “He is my Senpai.” in English.
However, this explanation doesn’t address how with what to call / address to Senpai as a courtesy title or addressing word in school, office, and business, social, cultural circles.
Is it true that there is no equivalent or alternative to “Senpai” as addressing word in English? If there are, how do you call?