細い

1. Origins, structure, and basic meaning

• Structure: 細い, read ほそい, is an い-adjective for a small thickness in a long object or a narrow width in a road or passage.
• Basic usage: 細い糸 is thin thread, while 細い道 is a narrow road; the natural English choice follows the object.

2. Common pitfalls and similar expressions

• Thickness and width
  • With thread it concerns thickness, while with a road it concerns the width available for passage, so one English gloss does not fit every object.
• Focus compared with 狭い
  • 細い focuses on a slender or narrow shape; 狭い more directly judges a space as cramped or lacking room.