惰性
1
force of habit
高校時代からつきあっている彼氏はいるものの、つきあいが惰性になっていると感じ、不満をつのらせている。
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
inertia
See also:
慣性 (かんせい)
Other forms
堕性 【だせい】 (search-only kanji form)