January
noun
Since the kanji 月 mean both moon and month (because a moon cycle is about a month, presumably), what is the number one month? In English we have an actual name for it, and that name is January.
いちがつ
This is a jukugo word, which usually means on'yomi readings from the kanji. 月 has two on'yomi readings, but it always uses the がつ reading in the names of the months, so here's a mnemonic to help you remember that: January always gives you itchy guts (いちがつ). It's a weird affliction that comes around every January and makes your guts incredibly itchy. Probably due to all that overindulgence over the new year.
ウェディングパーティーは一月でした。
The wedding reception was in January.
一月は、デザイナーとのミーティングがある。
In January, we have a meeting with the designer.
一月には、このホテルを出て行くことにしたよ。
I decided to leave this hotel in January.