other N2 uncommon casualpolitewritten

〜同士 — among / between fellow ~ / each other

〜同士・どうし

Meaning

(among) fellow ~ / ~ with one another / people of the same kind — a suffix marking mutual relations within a group of the same type

学生がくせい同士どうしで問題もんだいを解とき合あった。

The students worked through the problems with one another.

Attaches to	Form	Example
Noun (a person or group type)	N + 同士どうし	友達ともだち同士どうし / 恋人こいびと同士どうし

似にた者もの同士どうし、すぐに仲なかよくなった。

Being two of a kind, they hit it off right away.

子こども同士どうしのけんかに、親おやが口くちを出だすべきではない。

Parents shouldn't butt into squabbles between the kids themselves.

Marks reciprocal relations among members of the same category — お互たがいに ('each other') captures the same mutuality adverbially. 似にた者もの同士どうし ('birds of a feather') is a common set phrase.

Jengo shows 〜同士 the way you actually meet it: inside real Japanese sentences, so it sticks instead of staying an abstract rule.

Sources Compiled with reference to A Dictionary of Advanced Japanese Grammar.