also: ぢゅう
suffix
throughout; all ... long
Attaches to time nouns to mean 'throughout the entire period'. Common with 一日中, 一晩中, 年中.
彼は一晩中勉強していた。
He was studying all night long.
この店は年中無休です。
This shop is open all year round.
suffix
within; by the end of
Used with time nouns followed by に to mean 'within that period' or 'by the end of it'. Common with 今日中に, 今週中に.
今日中にこの仕事を終わらせてください。
Please finish this work within today.
今週中にレポートを提出しなければならない。
I have to submit the report by the end of this week.
suffix
all over; throughout (a place)
Attaches to place nouns to mean 'all over' or 'throughout that area'. Common with 世界中, 町中.
そのニュースは世界中に広まった。
The news spread all over the world.
町中がお祭りムードだった。
The whole town was in a festive mood.
suffix
Attaches to group nouns to mean 'all members of that group'. Common with 家族中, 学校中.
家族中で旅行に行った。
The whole family went on a trip.
学校中がその話題で持ちきりだった。
The whole school was buzzing about that topic.
Historical kana spelling; rarely used in modern writing.
Also a suffix, but ちゅう often means 'during' or 'in the middle of' (e.g., 会議中), while じゅう emphasizes 'throughout the entire period/area/group'.
The suffix じゅう derives from the kanji 中 (middle/inside), with a rendaku-like voicing from ちゅう. It is used to express the idea of 'throughout' or 'all over'.