親しい

1. Origins, structure, and basic meaning

• Structure: 親しい is the i-adjective したしい, describing a close personal relationship.
• Basic usage: In 学生時代から親しい友人と久しぶりに会った。, the speaker meets a friend they have been close to since their school days after a long time apart.

2. Common pitfalls and similar expressions

• Becoming close
  • 親しくなった changes the adjective's final い to く to express becoming close. The と in 先生と identifies the other person in that relationship.