• 字じ — character, letter
• 名字みょうじ — surname
• 漢字かんじ — Chinese character
• 数字すうじ — number character
• 文字もじ — written character
• 赤字あかじ — deficit
• 活字かつじ — printed type
• 字幕じまく — subtitles / captions

“字” originally pictured a child learning under a roof, which later came to represent written characters. Today, it is central to words related to writing systems, names, numbers, and subtitles.