Sometimes the kanji says it all. Though in most cases it is largely impossible to foretell a character’s meaning from its shape — 田 (window?), 今 (bus stop?), 無 (cockroach in motion?) — the semantics of this one cuts right through you: 中.
Read naka, chū or jū, 中 captures the complex meaning of being within, between or in the middle of something. In its most straightforward sense, it translates simply as “in”: 家の中 (ie no naka, in the house), カバンの中 (kaban no naka¸ in the bag) or, more metaphysically, 心の中 (kokoro no naka, in the heart). Even when outside, you can still be “in” something, for instance, 雨の中 (ame no naka, in the rain).
The “middle” meaning of 中 becomes apparent in terms like 中指 (nakayubi, the middle finger or toe) and 中庭 (nakaniwa, a courtyard between buildings). One of my favorite “middle” expressions is 中古 (chūko), which means “second-hand” and literally translates as “middle-old.”
Speaking of which, when you are neither young nor feel really ancient yet, you probably qualify as 中年 (chūnen, middle age), not to be confused with 中世 (chūsei, the Middle Ages). Another term to express in-between states is 中途半端 (chūtohanpa), referring to something in a neither-fish-nor-fowl kind of situation.
Since being in the middle of something is also a salient geographic property, 中 is a frequent component in place names. For instance, there’s 中東 (chūtō, the Middle East) and, of course, 中国 (chūgoku, China). This latter is not to be mistaken with 中国地方 (chūgoku chihō), the Chugoku region in the western part of Japan.
Related and yet somewhat different in meaning are a number of 中 expressions referring to the concept of “intermediateness.” Here the term is to be interpreted as a member of the triad 小 (shō, small), 中 (chū, medium) and 大 (dai, big). These are used to classify things in terms of size, in a similar way to S, M and L in English.
In addition, 中 can also denote an intermediate stage between strong and weak, as in the cooking expressions 強火 (tsuyobi, high flame), 中火 (chūbi, medium flame), and 弱火 (yowabi, low flame). The term 中火nicely illustrates that the “medium” meaning is only contained in the chū reading: Even though nakabi would be a more “logical” pronunciation, given that naka belongs to the same lexical stratum as –bi, it is blocked here because naka just can’t convey the idea of intermediateness.
Reading also matters when 中 takes on yet another meaning. When something is all over the place, this can be expressed by using 中 as a suffix. The point is that in such cases, it is not read chū but jū. An example is 部屋中 (heya-jū), which is not just about being “in” the room, but being all over it, as in the case of toys, books or — god forbid — cockroaches in motion. Of course, the same trick can be done with larger entities, such as 町中 (machi-jū, throughout town), 日本中 (nihon-jū, all over Japan) and世界中 (sekai-jū, in the whole wide world).
Apart from its spatial qualities, 中 is also customarily used to anchor things in time. 今週中に (konshū-chū ni), for instance, refers to something to be done within this week, and 今日中に (kyō-jū ni) means it should be finished by the end of today. Note that the chū/jū distinction gets somewhat arbitrary here.
If we drop the particle ni, we get back to the idea of being right in the middle of, which for time works just as well. A greater number of this type of 中 constructions are used in the busy world of business: 営業中 (eigyō-chū, open), 準備中 (junbi-chū, opening soon), 会員募集中 (kaiin boshū-chū, looking for new members), or キャンペーン実施中 (kyanpēn jisshi-chū, campaign now underway).
But thinking about it, ordinary life is also a quite busy affair. Most of the time we’re仕事中 (shigoto-chū, working), and when we’re not, we’re 休憩中 (kyūkei-chū, taking a break). We need to eat and sleep, and when we’re “at” these, we are 食事中 (shokuji-chū, eating) and 爆睡中 (bakusui-chū, sleeping like a log). Be careful not to become アル中 (aru-chū), because this term, an abbreviation of アルコール中毒 (arukōru chūdoku), doesn’t mean that you’re just boozing, but that you are an alcoholic.
Other states we may find ourselves “in” include 検討中 (kentō-chū, considering) and 確認中 (kakunin-chū, confirming), 瞑想中 (meisō-chū, meditating) and 分析中 (bunseki-chū, analyzing), 考え中 (kangae-chū, thinking) and 悩み中 (nayami-chū, brooding).
Truly, it’s some busy 世の中 (yononaka, world) — and we are right ど真ん中 (domannaka, in the middle) of it.