neap (adj.)

"low, lowest," applied to tides which have the least difference of height between the flood and ebb, late 15c., from Old English nepflod "neap flood," the tide occurring at the end of the first and third quarters of the lunar month, in which high waters are at their lowest, of unknown origin, with no known cognates (Danish niptid probably is from English). Original sense perhaps is "without power." As a noun from 1580s, "a neap tide," also sometimes in modern use "the ebb or lowest point of a tide."

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Definitions of neap

neap (n.)
a less than average tide occurring at the first and third quarters of the moon;
Synonyms: neap tide