The Collaborative International Dictionary of English v.0.48:

Arena \A*re"na\, n.; pl. E. Arenas; L. Aren[ae]. [L. arena,
   harena, sand, a sandy place.]
   1. (Rom. Antiq.) The area in the central part of an
      amphitheater, in which the gladiators fought and other
      shows were exhibited; -- so called because it was covered
      with sand.
      [1913 Webster]

   2. Any place of public contest or exertion; any sphere of
      action; as, the arenaof debate; the arena of life.
      [1913 Webster]

   3. (Med.) "Sand" or "gravel" in the kidneys.
      [1913 Webster]

WordNet (r) 3.0 (2006):

arena
    n 1: a particular environment or walk of life; "his social
         sphere is limited"; "it was a closed area of employment";
         "he's out of my orbit" [syn: sphere, domain, area,
         orbit, field, arena]
    2: the central area of an ancient Roman amphitheater where
       contests and spectacles were held; especially an area that
       was strewn with sand
    3: a large structure for open-air sports or entertainments [syn:
       stadium, bowl, arena, sports stadium]
    4: a playing field where sports events take place [syn: arena,
       scene of action]

Moby Thesaurus II by Grady Ward, 1.0:

98 Moby Thesaurus words for "arena":
   academic discipline, academic specialty, ambit, amphitheater,
   applied science, area, art, assembly hall, auditorium, back,
   backdrop, background, bailiwick, beat, border, borderland, chapel,
   cincture, circle, circuit, circus, close, concern, concert hall,
   confine, container, convention hall, coop, court, courtyard,
   curtilage, dance hall, delimited field, demesne, department,
   department of knowledge, discipline, distance, domain, dominion,
   enclave, enclosure, exhibition hall, field, field of inquiry,
   field of study, fold, gallery, ground, hall, hemisphere,
   hinterland, judicial circuit, jurisdiction, lecture hall, list,
   locale, march, meetinghouse, mise-en-scene, music hall,
   natural science, ology, opera house, orb, orbit, pale, paling,
   park, pen, precinct, province, pure science, quad, quadrangle,
   realm, rear, ring, round, scene, science, setting, social science,
   specialty, sphere, square, stadium, stage, stage set,
   stage setting, study, technicology, technics, technology, theater,
   toft, walk, yard



The Jargon File (version 4.4.7, 29 Dec 2003):

arena
 n.

    [common; Unix] The area of memory attached to a process by brk(2) and sbrk
    (2) and used by malloc(3) as dynamic storage. So named from a malloc:
    corrupt arena message emitted when some early versions detected an
    impossible value in the free block list. See overrun screw, aliasing bug
    , memory leak, memory smash, smash the stack.


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

arena

    The area of memory attached to a Unix process
   by the brk and sbrk system calls and used by malloc as
   dynamic storage.  So named from a "malloc: corrupt arena"
   message emitted when some early versions detected an
   impossible value in the free block list.

   See overrun screw, aliasing bug, memory leak, memory
   smash, smash the stack.

   [Jargon File]

   (1995-12-28)


The Devil's Dictionary (1881-1906):

ARENA, n.  In politics, an imaginary rat-pit in which the statesman
wrestles with his record.


U.S. Gazetteer Places (2000):

Arena, WI -- U.S. village in Wisconsin
   Population (2000):    685
   Housing Units (2000): 269
   Land area (2000):     1.089850 sq. miles (2.822699 sq. km)
   Water area (2000):    0.004581 sq. miles (0.011865 sq. km)
   Total area (2000):    1.094431 sq. miles (2.834564 sq. km)
   FIPS code:            02550
   Located within:       Wisconsin (WI), FIPS 55
   Location:             43.166108 N, 89.907305 W
   ZIP Codes (1990):     53503
   Note: some ZIP codes may be omitted esp. for suburbs.
   Headwords:
    Arena, WI
    Arena