remainder

1. Origins, structure, and basic meaning

• Structure: 余 relates to what remains or is available beyond immediate needs; 余裕 is read よゆう.
• Basic usage: 余る(あまる) means to be left over after use or distribution; 余分(よぶん) refers to an amount beyond what is needed.

2. Common pitfalls and similar expressions

• Leeway and excess
  • 時間に余裕がある means there is time to spare. It emphasizes having room in the schedule, not simply having some unused time.
  • 余分な説明 is unnecessary explanation, whereas 余分に一足 can mean an extra pair packed as a precaution. The evaluation conveyed by 余分 depends on context.