The Collaborative International Dictionary of English v.0.48:

Kneeler \Kneel"er\, n.
   1. One who kneels or who worships by or while kneeling.
      --Tennyson.
      [1913 Webster]

   2. A cushion or stool to kneel on, such as one attached to a
      pew in a church.
      [1913 Webster]

   3. (Eccl. Hist.) A name given to certain catechumens and
      penitents who were permitted to join only in parts of
      church worship.
      [1913 Webster]

WordNet (r) 3.0 (2006):

kneeler
    n 1: a person in a kneeling position
    2: a board (sometimes cushioned) for someone to kneel on