胸襟

1. Origins, structure, and basic meaning

• Structure: 胸襟 (きょうきん) means one's inner thoughts; idiom 胸襟を開く means speaking with an open heart.
• Basic usage: 胸襟を開いて frames an honest mutual discussion; 胸襟を開き frames openness before concerns are exchanged at formal talks.

2. Common pitfalls and similar expressions

• Openness in personal discussion and formal talks
  • In both examples the full idiom matters more than the noun alone. 開いて and 開き connect to later clauses and do not describe physically opening the chest.