Same Day, The Same Day
noun
You have the same day, which comes out to same day. Note that this word is quite formal. To say the same day more casually, just use 同じ日!
どうじつ
This is a jukugo word, which usually means on'yomi readings from the kanji. Since 日 has two on'yomi readings, here's a mnemonic to help you remember which one to use: On the same day, you once ate two entire doughnuts. Gee, two (どうじつ) on the same day? How did that feel?
DVDとCDが同日にリリースされた。
The DVD and CD were released on the same day.
同日にシアトルとポートランドに行けますか？
Can you go to Seattle and Portland in the same day?
アポロ１１号が月へ行ったのは、父が三十才になった日と同日だ。
Apollo 11 went to the moon on the same day as my father turned thirty.