熱心

1. Origins, structure, and basic meaning

• Structure: 熱心 (ねっしん) describes earnest, diligent engagement. The examples use adverbial and attributive forms.
• Basic usage: A woman practices pronunciation diligently; an enthusiastic reader sends detailed feedback.

2. Common pitfalls and similar expressions

• Diligent manner of practice and enduring attitude of a person
  • 熱心に modifies 練習している; 熱心な modifies 読者. The core is sustained commitment rather than momentary excitement.