expression, ichidan verb
put in a word for; second; support
Used when someone adds their own supportive comment or recommendation to help another person's proposal, request, or cause.
彼が企画を提案したとき、私も口を添えて賛成した。
When he proposed the plan, I also put in a word and agreed.
部長に頼みごとをするなら、先輩に口を添えてもらうといいよ。
If you're going to ask the department head for something, it's good to have a senior colleague put in a word for you.