"말문을 열다" is an idiom. Number one rule for idioms: just take it in. There's nothing to be gained by hashing it out into smaller units.Hi, I have another vocabulary another question.
What is 말문?
잠시 후 메그가 아까와는 사뭇 다른 목소리로 말문을 열었다.
I am more interested in the literal meaning of the highlighted word, rather than the sentence translation.