Japanese word indicating a time of day. When it is suffixed to numbers by itself, it usually means "o'clock". However, it also conveys general notions of time and is used in words like ichinichi-ji (all day). Ji is not used alone -- it's basically a suffix or prefix.

Ima wa san-ji desu.
It's now 3:00.

Nan-ji ni okimashita ka.
What time did you wake up this morning?

Ichinichi literally means "one day". However, ichinichi-ji means "all day", i.e. all the hours in the day.

Kyoo wa okimasen yo. Ichinichi-ji nemashita yo.
I didn't wake up today...I slept all day!

Written ji, with the kanji for "time; hour".