Grammar Info
N3 Lesson 9: 22/22

同士(どうし)
fellow・with each other, mutually, between・among, together・with

Structure
Noun + 同士
Noun + 同士 + + Noun
Details
Register Standard
使用域 一般
Information
同士(どうし) ‘fellow’ is a noun that may be used in the same was as a 接尾語(せつびご) (suffix). When used this way, it conveys things that are ‘mutually (A)’, ‘fellow (A)’, or ‘(A) together’.
To use 同士(どうし), attach it directly to the end of another noun, before expressing further information about that ‘mutual’ relationship. Alternatively, (noun + 同士(どうし) + の + noun) is also common, and expresses that noun (B) is a grouped form of noun (A).
  • これは弁護士(べんごし)同士(どうし)話(はな)しなので勝手(かって)入(はい)って来(こ)ないで下(くだ)さい
    This is a conversation between lawyers, so please don't barge in.
  • 家族(かぞく)同士(どうし)会話(かいわ)するときほとんど日本語(にほんご)です
    When we talk between family members, we mostly use Japanese.
  • 彼(かれ)は友達(ともだち)同士(どうし)約束(やくそく)破(やぶ)った。
    He broke a promise that was made between friends.
  • お互(たが)い大人(おとな)同士(どうし)なんだから、落(お)ち着(つ)いて話(はな)し合(あ)おうよ。
    We are fellow adults, so let's calm down and talk about this.
同士(どうし) is used most often to express two different types of ‘mutuality’. These are as follows:
種類(しゅるい) - Type. (A) is the same type as (B).
関係(かんけい) - Relationship. (A) shares the same relationship as (B).
  • あなたたちは本当(ほんとう)似(に)たもの同士(どうし)ね。
    You guys are really similar (in personality).
  • それは兄弟(きょうだい)同士(どうし)問題(もんだい)でしょ?私(わたし)巻(ま)き込(こ)まないで
    That is an issue between siblings, isn't it? Don't pull me into it.
Caution
同士(どうし) is most frequently used to highlight ‘people’, or ‘living things’ that share some type of relationship, rather than inanimate objects. An easy way to remember this is that the 士(し) kanji in this word means ‘gentleman’. However, it may occasionally be seen in reference to inanimate objects as well.
  • この糊(のり)は紙(かみ)同士(どうし)よくくっつきますプラスチック同士(どうし)あまりくっつかないです
    This glue sticks really well between paper, but between plastic, it does not stick well. (Natural, but not very common)
  • プロ格闘家(かくとうか)同士(どうし)戦(たたか)いは見(み)ていて楽(たの)しい。
    Watching a fight between two professional martial artists is fun. (Natural)
Slow Male
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キリンは雄(おす)同士(どうし)が喧嘩(けんか)をする時(とき)互(たが)いに長(なが)い首(くび)で打(う)ち合(あ)う
When male giraffes fight among themselves they hit each other with their long necks.
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そのため、日本(にほん)の企業(きぎょう)会社(かいしゃ)同士(どうし) 協力(きょうりょく)が以前(いぜん)よりも必要(ひつよう)だ。
Because of that, cooperation among Japanese companies is needed more than before.
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負(ま)けた者(もの)同士(どうし)で飲(の)みに行(い)こうよ!
Those among us who have lost, let's go drinking!
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