大切

1. Origins, structure, and basic meaning

• Structure: 大切 (たいせつ) evaluates something as precious or important. 大切に is adverbial; 大切だ is predicative.
• Basic usage: 大切に使う describes careful treatment of a received watch; 大切だ judges keeping promises important.

2. Common pitfalls and similar expressions

• Treating an object with care and judging an action important
  • The adverb modifies 使う; the predicate evaluates 約束を守ること as a whole. Choose “precious” or “important” according to the evaluated target.