幼稚

1. Origins, structure, and basic meaning

• Structure: 幼稚(ようち) describes immature thought or behavior and forms a predicate with 幼稚だ.
• Basic usage: It is used critically of something lacking maturity, such as the attitude or excuse in the examples.

2. Common pitfalls and similar expressions

• The judgment differs from 幼い
  • 幼い(おさない) can simply refer to being young, whereas 幼稚 more strongly evaluates something as immature. It can describe an adult's behavior too.
• Noun modification and connection
  • 幼稚な言い訳 uses な to describe the excuse. In 幼稚で、誰も納得しなかった, で connects that assessment to the following result.