for example, 죽음 is death but 죽기 is action of dieing.

When you add ㅁ/음 to a verb, it makes it a noun but it also makes it a separate word which you can usually find in a dictionary. This form is not what you would use in every-day korean. For example: 가르치다 - to teach 가르침 - the teaching 오다 - to come 옴 - the coming However, if you add ~기 to a verb, you have a noun and it's much more casual and used more often in every-day korean. This is the form you wouldn't find in a dictionary, for example: 만나다 - to meet 만나기 - the noun form of 'to meet' 죽이다 - to kill 죽이기 - the noun form of 'to kill'

There are actually three ways to turn a verb into a noun form. 1. -는 것 - used the most widely for the broadest of cases. 먹는 것 (eating, or foodstuff), 2. -기 - 1) used for well established activities (책 읽기, 음악 듣기), 2) makes idiomatic expressions (하기(가) 싫다, 성공하기(가) 어렵다, 잊어버리기(가) 쉽다). 3. -ㅁ - more suited to formal or literary contexts than daily life (도와주심에 감사드립니다 = formal way of saying 도와주셔서 고마워요). It tends to make the noun conceptual or thoughtful (인내함, 기다림). It also appear in existing nouns: 죽음 = death. 삶 = life, 꿈 = dream. 잠 = sleep, etc. There's no simple rule as to which form to use when. In many cases, both -는 것 and -기 work equally well. But here are some basic guidelines. 1. use -기 for idiomatic phrases (-기(가) 쉽다/어렵다/좋다/싫다, etc). 2. use -기 for common activities, especially with a clear purpose: 영화 보기(를) 좋아하세요? 3. use -는 것 for things that happen on their own: 누군가가 뛰어가는 것이 보였다 (can't use -기 in this case) 4. use -ㅁ when you conceptualize an action in a writing context, like an essay for example. 5.use -는 것 if you're not sure, as it's the most general expression.