The Collaborative International Dictionary of English v.0.48:
Retard \Re*tard"\, n.
1. Retardation; delay.
2. A mentally retarded person. [Colloq. and disparaging]
3. a person who is stupid or inept, especially in social
situations. [Colloq. and disparaging]
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.