old

1. Origins, structure, and basic meaning

• Structure: 古 expresses being old or worn; its on-reading is こ, and 古い is read ふるい.
• Basic usage: 古い can describe an old clock tower or worn bag, while 稽古, read けいこ, means practice or training.

2. Common pitfalls and similar expressions

• Becoming old or worn
  • 古くなった describes the change of becoming old or worn. 古い changes to 古く before joining なった.