What is "retard of the tide"

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.