#1 and #2 are sets of synonyms, while the #3 is not.
1. 고뇌, 번뇌
- 고뇌: 고(pain, suffering) + 뇌(anguished mind) => be tormented, agonize.
- 번뇌: 번(disturbing thoughts) + 뇌 => anguish with guilt, fear, anxiety, etc.
* 고뇌 emphasizes agony and pain, while 번뇌 implies a disquieted mind with endless disturbing thoughts.
2. 배척, 배타, 배제
- 배척(not 배책): 배(exclude, keep out) + 척(antagonize, attack) => kick out; drive out.
- 배타: 배 + 타(others) => exclude and oppose outsiders. 배타 is used as part of other words, like 배타적/배타성.
- 배제: 배 + 제(eliminate, discard) => discriminate against, keep out, exclude.
* All in #1 and #2 are nouns, and can make a verb with -하다 (and -되다 for some), except 배타.
* 배타 is not used independently or as 배타하다.
3. 방부제, 보완제 (unrelated words)
- 방부제: 방(resist, guard against) + 부(decay, putrefication) + 제(agent) => preservative.
- 보완재(not 제): 보(supplement, complement) + 완(complete) + 재(goods) => supplementary goods.
* 보완제 doesn't make sense because 제 means an agent implying a specific function which 보완 doesn't have.
* Related to 보완재 is 연관재(related goods) which consists of 대체재(replacement goods) and 보완재.