old friendship; long-standing acquaintance
Refers to a friendship or relationship from the past, often rekindled or remembered. Common in set phrases like 旧交を温める (to renew an old friendship).
We renewed our old friendship at the class reunion.
I have a long-standing acquaintance with him.
交友 is a general term for friendship or companionship, not necessarily old or past.
Standard kanji form; used in news and formal writing.
Rarely used kanji form; learners should recognize but not produce it.
Compound of 旧 (old, former) and 交 (intercourse, relationship). The meaning is transparent from its components.