noun
bosom friend; close friend; intimate friend
A formal or literary term for a very close, trusted friend; carries a slightly elevated, heartfelt tone compared to 親友.
彼は私の心友であり、何でも話せる存在だ。
He is my bosom friend, someone I can talk to about anything.
心友との絆は、時間が経っても変わらない。
The bond with a close friend remains unchanged over time.