NOUN (2)

1. spiritual leader of a Jewish congregation; qualified to expound and apply Jewish law;

2. a Hebrew title of respect for a Jewish scholar or teacher;

The Collaborative International Dictionary of English v.0.48:

Rabbi \Rab"bi\ (r[a^]r"b[imac] or r[a^]r"b[i^]; 277), n.; pl.
   Rabbis (r[a^]r"b[imac]z or r[a^]r"b[i^]z) or Rabbies.
   [L., fr. Gr. "rabbi`, Heb. rab[imac] my master, from rab
   master, lord, teacher, akin to Ar. rabb.]
   Master; lord; teacher; -- a Jewish title of respect or honor
   for a teacher or doctor of the law. "The gravest rabbies."
   --Milton.
   [1913 Webster]

         Be not ye called Rabbi, for one is your Master, even
         Christ, and all ye are brethren.         --Matt. xxiii.
                                                  8.
   [1913 Webster]

WordNet (r) 3.0 (2006):

rabbi
    n 1: spiritual leader of a Jewish congregation; qualified to
         expound and apply Jewish law
    2: a Hebrew title of respect for a Jewish scholar or teacher