One Month
noun
Remember the 〜ヶ月 counter? Replace the 〜 with a one and this becomes one month.
いっかげつ
一 uses the on'yomi you learned with it, but gets shortened, so watch out for that. The rest is as you learned it!
クリスマスまであと一ヶ月ですね！
It's one more month until Christmas!
一ヶ月半、日本で学校に行くんです。
I'll be going to school in Japan for one and a half months.
一ヶ月間、家から出ずにゲームをした。
I played games at home without going outside for a month.