neap

The second and fourth quarters of the moon produce a neap tide, when the different between high and low, ebb and flow, is the least of the month. The strip of shore where murderers might be buried is at its most narrow, and thus is, I suppose, the safest part of that safe zone not properly belonging to either land or sea. Fitting that it is the the even-numbered quarters, smooth rather than the pointed, odd numbers: Six of one, half a dozen of the other. Not much to choose between the high mark and the low mark is the entire point.

The word comes from Old English nepflod, and, like many words about country things and things close to the rhythms of nature's mysterious processes, it has not changed much in the journey to Modern English. Whence it comes to Old English is apparently not known. It seems always to have been more or less as it is now.