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).
同窓会で旧交を温めた。
We renewed our old friendship at the class reunion.
彼とは旧交がある。
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.