flood-gate n.

Old English flōd "a flowing of water, tide, an overflowing of land by water, a deluge, Noah's Flood; mass of water, river, sea, wave," from Proto-Germanic *floduz "flowing water, deluge" (source also of Old Frisian flod, Old Norse floð, Middle Dutch vloet, Dutch vloed, German Flut, Gothic flodus), from suffixed form of PIE verbal root *pleu- "to flow" (also the source of flow). In early modern English often floud. Figurative use, "a great quantity, a sudden abundance," by mid-14c.

"opening, entrance," Old English geat (plural geatu) "gate, door, opening, passage, hinged framework barrier," from Proto-Germanic *gatan (source also of Old Norse gat "opening, passage," Old Saxon gat "eye of a needle, hole," Old Frisian gat "hole, opening," Dutch gat "gap, hole, breach," German Gasse "street, lane, alley"), of unknown origin. Meaning "money collected from selling tickets" dates from 1896 (short for gate money, 1820). Gate-crasher is from 1926 as "uninvited party guest;" 1925 in reference to motorists who run railway gates. Finnish katu, Lettish gatua "street" are Germanic loan-words.