軽い

1. Origins, structure, and basic meaning

• Structure: 軽い is read as かるい and is an い-adjective for something low in weight or limited in degree or burden.
• Basic usage: Physical weight appears in 箱が軽い, while low-intensity activity appears in 軽い運動.

2. Common pitfalls and similar expressions

• Weight and degree
  • It applies to a physically light object and also to exercise with limited intensity or burden.
• Difference from 軽やか
  • 軽い broadly means light in weight or degree; 軽やか describes movement or an impression as light and lively.