old friend; long-standing acquaintance
Refers to a person one has known for a long time, often since childhood or many years ago. Carries a warm, familiar tone.
He's an old friend from elementary school.
I met an old friend after a long time, and we had a great time reminiscing.
Standard kanji spelling.
Mixed kanji-kana spelling, common in everyday writing.
Compound of 古 (old) and 馴染み (familiarity, acquaintance). The exact historical derivation is uncertain, but the word has been used since at least the Edo period.