to speak; to talk (idiomatic expression). Often appears in phrases like 'not speak to someone'.
彼女はあの人とはもう口をきかないと言っている。
She says she won't speak to that person anymore.
友達となら、何でも口をきけるから安心だ。
I can talk about anything with my friends, so I feel at ease.
初対面なのに、彼はすぐに口をきいてくれた。
Even though we met for the first time, he immediately started talking to me.
to mediate; to act as a go-between; to put in a good word for someone (idiomatic).
部長が本社と口をきいてくれて、契約がまとまった。
The manager spoke to headquarters on our behalf, and the contract was finalized.
彼が二人の間に口をきいてくれたおかげで、仲直りできた。
Thanks to him intervening between the two, they were able to reconcile.
友人が店長に口をきいてくれて、席を用意してもらった。
A friend put in a good word with the manager and got us a table.