How to say "loneliness" in Japanese

• 孤独こどくJLPT N1approx.Common
  na-adjective, no-adjectiveCovers both solitude, the state of being alone, and the ache of loneliness or isolation. It suits describing a person's inner condition or way of life, as in reflections on a solitary existence.
  私はこの上うえなくさびしく、孤独こどくだ。↗

  I am as sad and lonely as can be.
• 一人ぼっちひとりぼっちCommon
  no-adjectiveEmphasizes being all by oneself, with a lonely, sometimes self-pitying or sympathetic feel. Typical when talking about a child with no friends to play with, or someone left on their own.
  一人ひとりぼっちで暮くらしたくはない。↗

  I don't want to live by myself.

Use 孤独 for solitude or isolation as a condition — the state of being alone and the ache that can come with it — and 「一人ぼっち」 when the point is being all by oneself, often with a lonely, pitiable feel.

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

• 孤独こどくsolitude
• 独りぼっちひとりぼっちaloneness
• 寂寥せきりょうloneliness
• ロンリネスloneliness
• 孤こbeing alone
• 寂しささびしさ(feeling of) loneliness
• 孤独感こどくかんsense of isolation
• ぼっちaloneness