'Tide' originally meant 'time' — like German 'Zeit.' The sea's rhythm became its meaning on the coast.
The alternate rising and falling of the sea, usually twice in each lunar day, due to the gravitational attraction of the moon and sun.
From Old English 'tīd' (time, period, season, hour), from Proto-Germanic *tīdiz (time, period), from PIE *deh₂y-ti- (a division), from *deh₂y- (to divide). The word originally meant 'time' — not water. 'Eventide' is 'evening-time,' 'Christmastide' is 'Christmas-time,' and 'tidings' are 'things