the occurrence of incoming water (between a low tide and the following high tide); "a tide in the affairs of men which, taken at the flood, leads on to fortune" -Shakespeare
a cataclysm resulting from a destructive sea wave caused by an earthquake or volcanic eruption; "a colossal tsunami destroyed the Minoan civilization in minutes"
an obvious change of public opinion or political sentiment that occurs without leadership or overt expression; "there was a ground swell of antiwar sentiment"