The Collaborative International Dictionary of English v.0.48:

Playground \Play"ground`\, n.
   A piece of ground used for recreation; as, the playground of
   a school.
   [1913 Webster]

WordNet (r) 3.0 (2006):

playground
    n 1: an area where many people go for recreation [syn: resort
         area, playground, vacation spot]
    2: yard consisting of an outdoor area for children's play

Moby Thesaurus II by Grady Ward, 1.0:

44 Moby Thesaurus words for "playground":
   archery ground, athletic field, badminton court, baseball field,
   basketball court, billiard parlor, bowling alley, bowling green,
   course, court, cricket ground, croquet ground, croquet lawn,
   diamond, fairway, field, football field, glaciarium, golf course,
   golf links, gridiron, gym, gymnasium, ice rink, infield, links,
   outfield, oval, playing field, playroom, polo ground, pool hall,
   poolroom, putting green, racecourse, racket court, rink,
   skating rink, soccer field, squash court, stretch, tennis court,
   track, turf



The Free On-line Dictionary of Computing (30 December 2018):

Playground

   A visual language for children, developed for Apple's Vivarium
   Project.  OOPSLA 89 or 90?