으면서

while doing, at the same time

Says that one person does two things at once: 들으면서 "while listening", 밥 먹으면서 "while eating", 웃으면서 "while smiling". The two actions must share the same subject, which is what separates it from other while-words. It also carries a second, contrastive sense — and yet, both at once — when the two facts clash: 맛있으면서 몸에 해로운 "delicious and yet terrible for you". Attaches to consonant stems; vowel stems take 면서.