Stories We Like: A Guide to the Comma
"Jewish doctor of religious law," late 15c. (in Old English in biblical context only; in Middle English also as a title prefixed to personal names), from Late Latin rabbi, from Greek rhabbi, from Mishnaic Hebrew rabbi "my master," from rabh "master, great one," title of respect for Jewish doctors of law + -i, first person singular pronominal suffix. From Semitic root r-b-b "to be great or numerous" (cf. robh "multitude;" Aramaic rabh "great; chief, master, teacher;" Arabic rabba "was great," rabb "master").
An influential sponsor; a patron: I see you got the gold tin; who's your rabbi?
[1932+; the dated instance has to do with post-office workers]
my master, a title of dignity given by the Jews to their doctors of the law and their distinguished teachers. It is sometimes applied to Christ (Matt. 23:7, 8; Mark 9:5 (R.V.); John 1:38, 49; 3:2; 6:25, etc.); also to John (3:26).