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Webster 1828 Edition

Noun.

A gate to be opened for letter water flow through, or to be shut to prevent it.

An opening or passage; an avenue for a flood or great body.

See also: flood-gate and flood gate

floodgate ‎(plural floodgates)

An adjustable gate or valve used to control the flow of water through a sluice.
(by extension) Anything that controls or limits an outpouring of people, emotion etc.

gate or valve

anything that controls or limits an outpouring