na-adjective
Describes something poorly made, of low quality, or lacking substance. Often used for objects, but can also describe ideas or plans that seem half-baked.
このおもちゃ、ちゃちですぐ壊れちゃった。
This toy was so cheaply made that it broke right away.
彼の提案はちゃちで、誰も賛成しなかった。
His proposal was flimsy, and no one agreed with it.
The origin is uncertain. It may be a sound-symbolic word (mimetic) suggesting something light or insubstantial, but the exact derivation is unclear.