深い

1. Origins, structure, and basic meaning

• Structure: 深い is read as ふかい and is an adjective for physical depth or for the strength of something impressed on the mind.
• Basic usage: It can directly state that a place is deep, or change to 深く to describe a memory or impression remaining deeply.

2. Common pitfalls and similar expressions

• Physical depth
  • 湖は深い describes the lake's actual depth and can support a warning even near the shore. Example: この湖は岸の近くでも深いので注意が必要です。
• Depth of an impression
  • 胸に深く残る figuratively means that words or a memory leave a strong, lasting impression. Example: 先生の言葉が胸に深く残りました。