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.