惰性|だせいdasei[0]heiban (flat)

1. nounforce of habit
   高校こうこう時代じだいからつきあっている彼氏かれしはいるものの、つきあいが惰性だせいになっていると感かんじ、不満ふまんをつのらせている。↗

   She has a boyfriend she's been going out with since high school but feels their relationship has become a matter of habit and is increasingly dissatisfied.
2. noun, physicsinertia

• Related慣性かんせいWrittenWritten physics term for a body's tendency to keep its state of motion, as in 「慣性の法則」; for carrying on out of sheer habit, 「惰性」 is the usual word.
• Antonym活性かっせいWrittenWritten chemistry term for how readily a substance reacts, and figuratively vitality; listed opposite 「惰性」 as liveliness against sluggish inertia.

For inertia in physics, use 「慣性」, as in 「慣性の法則」. For continuing something out of habit, use 「惰性」, as in 「惰性で続ける」. In chemistry, readiness to react is 「活性」.

Usage comparisons are AI-assisted and cross-checked by multiple models; for study reference only

1. 慣性かんせい。
2. 今いままでの習慣しゅうかん。