The Collaborative International Dictionary of English v.0.48:

parsec \par"sec\ (p[aum]r"s[e^]k), n. [From parallax second. See
   parallax second and annual parallax, under parallax.]
   (Astron.)
   A unit of length used in describing astronomical distances,
   equal to 3.26 light years, or 3.086 x 1013 km. Abbreviated
   pc. The derived units of kiloparsec (kpc, 1000 parsecs) and
   megaparsec (mpc, one million parsecs) are often found in
   discussion of astronomical distances.
   [PJC]

WordNet (r) 3.0 (2006):

parsec
    n 1: a unit of astronomical length based on the distance from
         Earth at which stellar parallax is 1 second of arc;
         equivalent to 3.262 light years [syn: parsec, secpar]

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

PARSEC

    An extensible language with PL/I-like syntax,
   derived from PROTEUS.

   ["PARSEC User's Manual", Bolt Beranek & Newman, Dec 1972].

   (2009-06-26)