續一切經音義 6.157

6.157

不憚（下徒旦反切韻憚怒也又惡也論語云過則勿憚改注云憚難也說文從心單聲也）。

Not fearing (不憚: the second [character] is *dan*, fanqie 徒旦. The Qieyun says: '憚 means anger; also, to hate.' The Analects says: 'When you make a mistake, do not shrink from correcting it (勿憚改).' The commentary says: '憚 means to consider difficult.' The Shuowen jiezi says it is derived from the heart radical 心 with 單 as phonetic).