How to say "indifference" in Japanese

• 中性ちゅうせいJLPT N2approx.Common
  no-adjectiveThis is really the word for neutrality — chemical, electrical, and similar technical senses. Its 'indifference' gloss is marginal: for an indifferent person or attitude it is seldom the word you want.
  リトマス紙しで溶液ようえきの液性えきせい（酸性さんせい、中性ちゅうせい、塩基性えんきせい）を調しらべるときは、リトマス紙しをすべて溶液ようえきに浸ひたすのではなく、紙かみの先端せんたんの部分ぶぶんだけを浸ひたします。↗

  When investigating the pH (acidic, neutral, alkaline) of a liquid, don't soak the litmus paper completely in the liquid but just put the end of the paper in it.
• 不熱心ふねっしんCommon
  na-adjective, nounCovers indifference as lack of enthusiasm or effort — a student or employee who shows little interest and seldom applies themselves. The indifference is a matter of attitude rather than facial expression.
• 不在ふざいJLPT N1approx.Common
  noun (suffix)This word really means absence — the fact of someone or something not being there. Its 'disregard' and 'indifference' glosses are indirect, and it is seldom the word you want for an indifferent attitude.
• 知らん顔しらんかおCommon
  noun, suru verb, intransitive verbCovers indifference as an outward show: an unconcerned, nonchalant air, often feigned, of someone pretending not to know or not to be involved. It is about the visible look, not the inner feeling.
  彼女かのじょは知しらん顔かおをした。↗

  She assumed an air of indifference.

Choose 不熱心 for indifference as lack of enthusiasm or effort, 「知らん顔」 for a visible, often feigned show of unconcern; 中性 is really 'neutrality' and 不在 'absence', so both are marginal for this sense.

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

• 中性ちゅうせいneutrality (incl. chemical, electrical, etc.)
• 不熱心ふねっしんindifference
• 無感情むかんじょうapathy
• 不在ふざいdisregard
• 知らん顔しらんかおunconcerned air
• 不感症ふかんしょうinsensitivity
• 知らぬ顔しらぬかおunconcerned air