The Collaborative International Dictionary of English v.0.48:

Leaflet \Leaf"let\, n.
   1. A little leaf.
      [1913 Webster]

   2. (Bot.) One of the divisions of a compound leaf; a foliole.
      [1913 Webster]

   3. (Zool.) A leaflike organ or part; as, a leaflet of the
      gills of fishes.
      [1913 Webster]

   4. A printed sheet of paper, of one page, or one sheet folded
      over, containing an advertisement, tract, or other notice,
      and usually distributed for free or included in the
      package with a purchased item.
      [PJC]

WordNet (r) 3.0 (2006):

leaflet
    n 1: a thin triangular flap of a heart valve [syn: cusp,
         leaflet]
    2: part of a compound leaf
    3: a small book usually having a paper cover [syn: booklet,
       brochure, folder, leaflet, pamphlet]