Albert Barnes on John 20:16

Jesus saith unto her, Mary. This was spoken, doubtless, in a tone of voice that at once recalled him to her recollection.

Rabboni. This is a Hebrew word denoting, literally,my great master. It was one of the titles given to Jewish teachers. This title was given under three forms: (a) Rab, or master--the lowest degree of honour. (b) Rabbi, my master--a title of higher dignity. (c) Rabboni, my great master --the most honourable of all. This title, among the Jews, was only given to seven persons, all persons of great eminence. As given by Mary to the Saviour, it was at once an expression of her joy, and an acknowledgment of him as her Lord and Master. It is not improbable that she, filled with joy, was about to cast herself at his feet.

(m) "Mary" Is 43:1, Jn 10:3