一切經音義 6.246

6.246

平坦（他旦反廣雅坦平也又云坦明也王弼注周易云坦坦無險阸烏介反蒼頡篇云坦著也說文云坦安也從土旦聲也）。

平坦 (level and flat: [tǎn is pronounced with the fanqie] 他旦. The Guangya says: 'Tǎn (坦) means level; it also says tǎn means bright.' Wang Bi's commentary to the Book of Changes says: 'Tǎntǎn means without perilous straits (阸, [pronounced with the fanqie] 烏介).' The Cangjie pian says: 'Tǎn means manifest.' The Shuowen jiezi says: 'Tǎn means peaceful; it derives from 土 with 旦 as phonetic.')