Japanese

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For pronunciation and definitions of アク – see the following entry.
あく
[noun] [from early 900s] lye, originally the clear alkaline liquid left after leaching wood ash in water
[noun] scum, the coagulated proteins and fats that gather on the surface of a pot of boiling food
[noun] [from 1700] components contained in vegetables that impart an acrid, astringent, or harsh flavor
[noun] [from 1909] アク: (by extension from the "flavor" sense) harshness as a characteristic of one's personality
Alternative spelling
灰汁
(This term, アク (aku), is the katakana spelling of the above term.)