確慥 Kanji
彼が間違っているのは確かです。 It is certain that he is wrong.
これは確か淡水魚だと思います。 I believe this fish is a freshwater fish.
確かに彼は信頼できます。 You can certainly rely on him.
窓が閉まっているか確かめとけ。 See that the window is closed.