• 口笛くちぶえ — whistle
• 口調くちょう — tone of voice
• 口紅くちべに — lipstick
• 口内炎こうないえん — mouth ulcer
• 口実こうじつ — excuse
• 口座こうざ — bank account

The character “口” is one of the simplest and most common kanji. It often refers to the physical mouth, but also appears in compound words about speech, entrances, and numbers of people.

口くちを 大おおきく開あけてください。
Please open your mouth wide.

新あたらしい口座こうざを 開ひらきました。
I opened a new bank account.