同士(どうし)Fellow, With each other, Mutually, Between, Among, Together, With

同士(どうし) 'fellow' is a noun that may be used in the same way as a 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).

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).

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.