agger

Noun

1. A double tide, particularly a high tide in which the water rises to a given level, recedes, and then rises again (or only the second of these high waters), but sometimes equally a low tide in which the water recedes to a given level, rises, and then recedes again
   • The phænomenon of long continued high water or double high water in estuaries is, we believe, not uncommon. [...] The first high water appears to be considered by the Dutch, in common language, as the real high water,...
   • A double tide or agger is a high tide consisting of two maxima of nearly the same height, separated by a relatively small depression; or a low tide consisting of two minima separated by a relatively small elevation. -...
   • [page 62:] As can be seen [...], once the water has reached the lowest level, it remains low for some time. After rising slightly, it then drops again and a second low tide follows. Only then does the water rise quickly...
2. Synonym of earthwork in ancient Roman contexts, particularly a defensive wall or mound.
   • By the Augustan period, however, the old ashlar circuit with its earthen agger was beginning to be dismantled in some places. - 2012, Seth G. Bernard, “Continuing the Deabte on Rome's Earliest Circuit Walls”, in Papers...

   Synonyms: earthwork in ancient Roman contexts particularly a defensive wall or mound