Source : Webster's Revised Unabridged Dictionary (1913)

Perennial \Per*en"ni*al\, a. [L. perennis that lasts the whole
   year through; per through + annus year. See {Per-}, and
   {Annual}.]
   1. ing or continuing through the year; as, perennial
      fountains.

   2. Continuing without cessation or intermission; perpetual;
      unceasing; never failing.

            The perennial existence of bodies corporate.
                                                  --Burke.

   3. (Bot.) Continuing more than two years; as, a perennial
      steam, or root, or plant.

   Syn: Perpetual; unceasing; never failing; enduring;
        continual; permanent; uninterrupted.

Perennial \Per*en"ni*al\, n. (Bot.)
   A perennial plant; a plant which lives or continues more than
   two years, whether it retains its leaves in winter or not.

Source : WordNet®

perennial
     n : a plant lasting for three seasons or more

perennial
     adj 1: lasting three seasons or more; "the common buttercup is a
            popular perennial plant" [ant: {annual}, {biennial}]
     2: lasting an indefinitely long time; suggesting self-renewal;
        "perennial happiness"
     3: recurring again and again; "perennial efforts to stipulate
        the requirements" [syn: {recurrent}, {repeated}]