China and Japan; Chinese-Japanese; Sino-Japanese
middle day (of a sumo tournament, theatrical run, etc.)
day of an equinox
「中日」 has another reading with different meanings.
中日関係は重要な課題だ。
China-Japan relations are an important issue.
中日の文化交流が盛んになっている。
Cultural exchange between China and Japan is thriving.
中日両国の経済的なつながりは年々深まっている。
The economic ties between China and Japan are deepening year by year.