How to say "seriousness" in Japanese

• 本気ほんきJLPT N1approx.Common
  no-adjective, na-adjectiveSeriousness as genuine intent or earnestness: it presents a person's seriousness as meaning what they say and committing to a plan, study, or relationship for real.
  ケンさん、君きみは本気ほんきかい。↗

  Are you on the level, Ken?
• 本腰ほんごしCommon
  nounSeriousness as strenuous effort: it frames being serious as a matter of the work you put in, fitting a context like a person or company getting down to business on a project.
  さて、本腰ほんごしを入いれてまじめな話はなしをしよう。↗

  Now let us get down to a serious talk.
• 真しんCommon
  nounGlossed simply as seriousness, yet on its own it is seldom the word you want: it rarely stands alone, doing its work inside compounds and set expressions, so for this sense prefer 本気.

Use 本気 for seriousness as genuine intent or earnestness, 本腰 for seriousness shown by putting real effort into a task, and treat 真 as marginal on its own, since it mostly lives inside other expressions.

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

• 本気ほんきseriousness
• 本腰ほんごしstrenuous effort
• 重大性じゅうだいせいimportance
• 本気度ほんきど(degree of) seriousness
• 真しんseriousness