• 四よん — four
• 四よっつ — four (general counter)
• 四人よにん — four people
• 四月しがつ — April
• 四角しかく — square
• 第四だいよん — the fourth (ordinal)

“四” comes from a pictograph combining the mouth radical and lines representing counting. Although it is a basic number, it carries cultural significance, as “よん” can sound like “し” (死), which means death. Because of this, the number four is sometimes avoided in settings like hospitals and hotels.

四よっつの りんごを 買かいました。
I bought four apples.

四月しがつに 入学にゅうがくしました。
I started school in April.