Welcome to the first month of the new year, which in Japan comes with the very straightforward name ichigatsu (一月) — literally, “month one”.
The numeral that is contained here, ichi (一, one), is rather essential in Japanese. It is the first character that children learn at school, and it is about the only one that consists of a single stroke if we discount katakana’s no (ノ) and two or three more obscure fellow Kanji. In contrast to its very simple shape, however, things can get a bit nasty when it comes to the varied readings of this little piece of minimal art.
When you count 1, 2, 3, you say ichi, ni, san, so that shouldn’t be a problem. The same holds for combinations with various (though not all) units of measurements, such as one second, one liter, or one paragraph, which would be ichi byō (一秒), ichi rittoru (一リットル), and ichi danraku (一段落), respectively. Many other combinations follow this pattern, including more abstract terms like ichiō (一応, for the time being, as far as it goes) and ichigai ni (一概に, [not] necessarily), where no real counting is involved.
In line with basic pronunciation rules, the reading of ichi may be coalesced with the word that follows, as in ikkai (一階, first floor) and ikko (一個, one item) or ippun (一分, one minute) and ippo (一歩, one step). There are a number of noncounting expressions formed this way, too. Thus there is issho (一緒, together), ippan (一般, general), issai (一切, not in the least), issei (一成, a friend of mine), and ippai (一杯), which is a little tricky because it can mean both “one drink” and “a lot.” Though the accent in each case is different, a coincidence which may be a source of misunderstanding and, surely in some cases, marital conflict.
Ichi can also appear in the second position of a compound. An example is the expression man[ga]ichi (万[が]一, by any chance, just in case), which literally means “one in 10,000.” It is a favorable component in reminders to take precautions against some sort of misfortune that may occur with a presumed likeliness of, well, one in 10,000, though in my experience the odds are usually higher. When something hasn’t quite met one’s expectations, this is called imaichi (今一, not really good), and a divorce in colloquial Japanese is known as batsuichi (バツイチ).
When used in second position, the reading of ichi may change to itsu, as in tōitsu (統一, unity), dōitsu (同一, sameness), and kinitsu (均一, evenness).
If some superlative achievement needs to be expressed, ichi can also attach to a given place name, as in nippon ichi (日本一, best in Japan) or sekai ichi (世界一, top of the world).
Another useful expression is ichiichi. This doubling of the numeral can be used to take issue with any sort of fussy or pedantic behavior. “Ichiichi monku iu na” (いちいち文句言うな, Stop nagging about each little thing!)” is what you could say in such cases — though it’s probably not best to use this one too much.
As with every decent kanji, ichi also has an indigenous Japanese reading. That’s where hito comes in. We find it in terms like hitoban (一晩, one evening), hitokoto (一言, one word), hitokuchi (一口, a mouthful of) and hitonigiri (一握り, a handful of). It is also used for counting groups of unspecified things or people, where you start with hitotsu (一つ) and hitori (一人), respectively.
Incidentally, hitori also means alone, as in hitorigurashi (一人暮らし, live alone) or hitoritabi (一人旅, travel by oneself). Ohitori sama (お一人様) is a polite expression to refer to customers without company and, more recently, to a new female lifestyle. Kind of confusing is that the same “one + person” combination in some cases switches back to the ichi reading. Examples are ichininmae (一人前, for one person; adult), ichininnori (一人乗り, one-passenger vehicle), and ichininshō (一人称, first person in the grammatical sense).
There are even more irregularities. The first day of the month, for instance, is called tsuitachi (一日), a reading that appears utterly unrelated to either “one” or “day,” though that’s how it is written. Both foreign and native learners take quite some time learning to resist the urge to read it ichinichi, which also exists and is written the same way, but means “one day,” not “day one.” To make things worse, there is ippi — a third possible reading. It’s the more casual alternative of tsuitachi and acceptable only for adults, normally in some sort of office situation.
The numeral also hides quite successfully in the time expressions ototoi (一昨日, the day before yesterday) and ototoshi (一昨年, the year before last). The concurring readings issakujitsu and issakunen are much more transparent, but rarely ever used.
As you can see from this rather lengthy discussion, the basics of ichi are quite simple. When it comes to the details though, there is only one way of getting it right: learning them, one by one.