Busy
い adjective
This is a single kanji with しい on the end, meaning it's an adjective. What's the adjective form of busy? It's also busy.
いそがしい
You're busy because you have to take care of your friend's ice ogres (いそが) this weekend. You don't know why you agreed to this, you were busy enough, but now you'll never get anything done running around taking care of these little ice ogres.
忙しくて、頭がクラクラしています。
I'm so busy that my head is spinning.
コウイチはとても忙しいので、コウイチからすぐメールの返事がくるとは思わないでください。
Don't expect a quick email response from Koichi, as he is really busy.
今日は忙しかったね。なんてったって、今日だけで千語も新しい日本語を学んだんだから。
Today was hectic. Just today, we learned 1000 new Japanese words.