Source : Webster's Revised Unabridged Dictionary (1913)

Gleaner \Glean"er\, n.
   1. One who gathers after reapers.

   2. One who gathers slowly with labor. --Locke.

Source : WordNet®

gleaner
     n 1: someone who picks up grain left in the field by the
          harvesters
     2: someone who gathers something in small pieces (e.g.
        information) slowly and carefully