1rare A tide occurring around the time of the new or full moon, when the high-water level is highest, the low-water level is lowest, and the difference between high and low tide is at its greatest; especially a high tide of this kind; = "spring tide". Also in figurative contexts.
2A river flood occurring in the spring.
Late Middle English; earliest use found in Geoffrey Chaucer (c1340–1400), poet and administrator. From spring + flood.