暂无解释，欢迎补充。

宋本廣韻

廣韻目次：去十遇小韻反切聲母韻母聲調平水韻等呼韻部韻攝罗马字䦌丑注徹虞去聲遇合口三等虞遇thryoh／thiuh

English

the door is wide open; directly in the front