一層

1. Origins, structure, and basic meaning

• Structure: 一層 (いっそう) combines one 一 and layer 層, with both the adverbial sense “even more” and the literal sense “one layer.”
• Basic usage: It intensifies improvement or counts a transparent film added to a surface.

2. Common pitfalls and similar expressions

• Degree and physical layer
  • 一層よく increases a degree, whereas 一層重ねる counts one actual layer placed on another.