From tachan; a hand mill; hence (figuratively) chewing -- grinding.
see HEBREW tachan
H2913. tachanah
טַחֲנָה noun feminine mill = foregoing, הַטּ קוֺל ׳בִּשְׁפַל Ecclesiastes 12:4 when the sound of the mill is low (compare 12:3, below verb above)
טחר (√ of following; compare Arabic eject; Aramaic טְחַר strain at stool, dysentery).