to get someone to say; to make someone say
to let someone say; to let someone speak out
to make a sound
息子に謝罪の言葉を言わした。
I made my son apologize to the neighbor.
この計画について言わしてほしい。
Please let me say what I really think about this plan.
あの弁護士はいつも相手証人に何か言わす。
That lawyer always gets the opposing witness to say something useful.