謂用言辭訂立相互信守之約定?！?a href="/hycd/l/l370453.htm" target="_blank">禮記·曲禮下》：“約信曰誓，涖牲曰盟?！薄?a href="/hycd/x/x259771.htm" target="_blank">荀子·富國(guó)》：“約信盟誓，則約定而畔無日?！薄?a href="/hycd/h/h257083.htm" target="_blank">淮南子·人間訓(xùn)》：“與民約信，非一日之積也；一舉而敗之，后不可復(fù)用?！?/p>