In Chinese 天tiān literally means day.
So today is called 今天（jīntiān）
with the same word "Jīn今" we can also say "this year" 今年jīnnián
Also tomorrow we say 明天míngtiān
， with the same word 明míng， we can use in the word next year, which is 明年Míngnián
In this video lesson, you'll see the complete saying of different days in organized chart.
(category- intro to Chinese - page 12)