固体

1. Origins, structure, and basic meaning

• Structure: The scientific noun 固体 (こたい) denotes the solid state of matter, which retains a definite shape and volume.
• Basic usage: Ice can be identified as a 固体, and phase change is expressed as 固体から液体へ.

2. Common pitfalls and similar expressions

• The solid state of matter
  • It names a state of matter contrasted with liquid and gas, not every object that happens to feel hard.