What does "retardation" mean?

Additional senses

1. 2.(Mus.) The keeping back of an approaching consonant chord by prolonging one or more tones of a previous chord into the intermediate chord which follows; -- differing from suspension by resolving upwards instead of downwards.
2. 3.The extent to which anything is retarded; the amount of retarding or delay. Retardation of the tide. (a) The lunitidal interval, or the hour angle of the moon at the time of high tide any port; the interval between the transit of the moon and the time of high tide next following. (b) The age of the tide; the retard of the tide. See under Retard, n.