The Collaborative International Dictionary of English v.0.48:

One-sided \One`-sid"ed\, a.
   1. Having one side only, or one side prominent.
      [1913 Webster]

   2. Hence: Limited to one side; favoring one person or side
      over another; partial; unjust; unfair; as, a one-sided
      view or statement. [WordNet sense 5] "Unguarded and
      one-sided language." --T. Arnold.

   Syn: biased, colored, slanted.
        [1913 Webster]

   3. Having one team or party greatly superior; strongly
      favoring only one side; uneven; imbalanced; unequal; as, a
      one-sided contest; -- of contests, generally. [WordNet
      sense 4]
      [PJC]

   4. (Bot.) Growing on one side of a stem; as, one-sided
      flowers.
      [1913 Webster]

   5. Using only one side, or having only one side usable; as,
      one-sided printing; one-sided film; -- used mostly of
      sheets of material used for printing or imaging.
      [PJC]

   6. Performed by only one party or side; -- of actions
      directly affecting more than one party. Opposite of
      multilateral. [WordNet sense 2]

   Syn: unilateral (vs. bilateral).
        [WordNet 1.5 +PJC]

   7. out of proportion in shape.

   Syn: ill-proportioned, lopsided.
        [WordNet 1.5]

   8. Not reversible or capable of having either side out; -- of
      cloth fabrics or clothing. Opposite of reversible.
      [WordNet sense 1]

   Syn: nonreversible.
        [WordNet 1.5] -- One`-sid"ed*ly, adv. --
        One`-sid"ed*ness, n.
        [1913 Webster]

WordNet (r) 3.0 (2006):

one-sidedly
    adv 1: in a unilateral manner; by means of one part or party;
           "they worked out an agreement unilaterally" [syn:
           unilaterally, one-sidedly] [ant: multilaterally]