The Collaborative International Dictionary of English v.0.48:

Retard \Re*tard"\, n.
   1. Retardation; delay.
      [1913 Webster]

   2. A mentally retarded person. [Colloq. and disparaging]
      [PJC]

   3. a person who is stupid or inept, especially in social
      situations. [Colloq. and disparaging]
      [PJC]

   Retard of the tide, or Age of the tide, the interval
      between the transit of the moon at which a tide originates
      and the appearance of the tide itself. It is found, in
      general, that any particular tide is not principally due
      to the moon's transit immediately proceeding, but to a
      transit which has occured some time before, and which is
      said to correspond to it. The retard of the tide is thus
      distinguished from the lunitidal interval. See under
      Retardation. --Ham. Nav. Encyc.
      [1913 Webster]