This is the 14067th most frequent Korean word.
머금고
"머금고" means "holding (something) in the mouth."
In this context, '머금고' signifies 'holding' as in keeping a smile on her face.
그녀는 입가에 미소를 머금고 나를 바라보았다.
She looked at me with a smile on her lips.
Here, '머금고' conveys the sense of metaphorically holding optimism.
그는 희망을 머금고 미래를 향해 나아갔습니다.
He proceeded toward the future holding onto hope.
In this sentence, '머금고' is used to describe the forest retaining water from the rain.