This is the 12639th most frequent Korean word.
대전시와
"대전시와" means "Daejeon City and."
Here, '대전시와' is used to indicate an associative relationship with another entity (서울시). It marks the city of Daejeon as part of the pair being discussed.
대전시와 서울시의 협력은 중요합니다.
The cooperation between Daejeon City and Seoul City is important.
In this sentence, '대전시와' serves to include Daejeon City as a collaborative entity involved in an action.
대전시와 함께 환경 보호 프로젝트에 참여했습니다.
I participated in an environmental protection project together with Daejeon City.
Here, '대전시와' implies a connection or relevance to Daejeon City with the issues being investigated.