fast

1. Origins, structure, and basic meaning

• Structure: The on reading is そく, and the kun readings are はやい, はやめる, すみやか. It has 10 strokes and relates to fast movement or the speed at which something moves.
• Basic usage: 速い is read はやい, and 速度 is read そくど.

2. Common pitfalls and similar expressions

• 速い / 速度
  • 速い means fast and is read はやい. It describes a train, person, or other moving subject as fast.
  • この列車は普通列車より速い。 means “This train is faster than the local train.”
  • 速度 means speed and is read そくど. It refers to the measured or perceived speed of movement or work.
  • 坂道では自転車の速度を落とした。 means “I reduced my bicycle's speed on the slope.”