ながす
to let flow, to set adrift
You stop holding it and let the water have it. The same Niagara なが as 流れる, except that somebody opened the gate. She did not wipe her face, she simply let them go: ながす.
Near 長い ながい, long, in sound and nothing else.
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Emaki is not affiliated with, or endorsed by, Kaishi 1.5k or its authors. The word, reading and meaning come from the Kaishi 1.5k deck, used with their permission. The mnemonic, the note and the kanji breakdown are original work, published under CC BY-SA 4.0.