bold : 侧重指面对困难或危险时勇往直前，勇于进取的勇敢精神。
- She was a bold and fearless climber.
- The newspaper made the bold move/took the bold step of publishing the names of the men involved.
brave : 含义广泛，指天生的勇敢，无所畏惧地面对困难与危险，侧重胆识与果断。
- a brave soldier
- It was a brave decision to quit her job and start her own business.
- She was very brave to learn to ski at 50.
- Of the three organizations criticized, only one was brave enough to face the press.
- Richards has made a brave attempt to answer his critics.
- This action will cause problems, despite the bank's brave talk/words about carrying on as if nothing had happened.
courageous : 正式用词，侧重指在一切情况下都有胆量，无所畏惧，强调基于道德信念，经深思熟虑后所产生的勇敢。
- It was a courageous decision to resign in protest at the company's pollution record.
- It was courageous of her to challenge the managing director's decision.
daring : 强调面临意外或危险时胆大心细，头脑冷静。褒义贬义均可用，贬义指胆大妄为。
- a daring escape
- This is a daring new film (= one willing to risk criticism) by one of our most original modern directors.
- She was wearing a fairly daring (= short) skirt that barely covered her bottom.
heroic : 正式用词，多指在战争或重大危险时，为他人为事业忘我献身的英雄气概。
- a heroic act/deed
- a heroic figure
- Rescuers made heroic efforts to save the crew.
- We watched our team's heroic struggle to win back the cup.
fearless : 语气肯定，侧重在危险时无所畏惧，毫无动摇。
- a fearless fighter
- Fearlessness stems from selflessness.; Only the selfless can be fearless.
- To go in for technical innovation, one must have the fearless spirit of a pathbreaker.