ます
to increase, to augment, to rise
Earth 土 going onto the heap and the heap gaining mass, and the river has been at it all week: ます.
増える ふえる is a thing increasing by itself and 増やす ふやす is you increasing it. 増す does both and is the more formal word.
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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.