空榫 [－－]

Jyutping hung1 seon2
Pinyin kōng sǔn

Definitions (Wiktionary)
  1. noun, Xiamen, Zhangzhou-Hokkien
    flaw; gap; faults (used against somebody); information that can be used against someone
    (syn.) 把柄, 空缝, 空縫
  2. noun, Taiwanese-Hokkien
    tenon