The Collaborative International Dictionary of English v.0.48:

11-plus \11-plus\ n.
   1. an examination taken by 11 and 12 year old students to
      select suitable candidates for grammar school. [formerly
      in England]

   Syn: eleven-plus
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

11-plus
    n 1: (formerly in Britain) an examination taken by 11 and 12
         year old students to select suitable candidates for grammar
         school [syn: eleven-plus, 11-plus]