What exactly are the differences between 大体, だいぶ and 大部分


Okay, those three make me very confused. To my understanding だいぶ is used when
it´s more than what you expected. 大体 should be more or less, but then where
comes 大部分? And is 大体 a lesser percentage than ほとんど?

Thank you very much for your help.



  * **だいぶ（大分）**  
An adverb meaning "becoming more advanced (= grown, progressed, lapsed
away...) than before", or if lacks the starting point it means "...than you/I
expect", or simply "considerably". It doesn't tell anything about percentage.

Synonyms are 相当, かなり, ずいぶん etc.

> 白髪が（○だいぶ／×大体／×大部分）増えてきた。

  * **だいたい（大体）**  
An adverb but sometimes used noun-like, "almost all/complete", "almost every
time/aspect" or "overall". You're right about "more or less" as in "more or
less finished".

The difference with **ほとんど** is that:

    * ほとんど is slightly closer to perfect in amount (I think)
    * だいたい lacks the use of "almost _something_ " 

> 彼は（○ほとんど／×だいたい）英雄だ。

    * ほとんど qualifying a noun means "nearly _noun_ " while だいたい is "approximately _noun_ " 

> 70%ということは（×ほとんど／○だいたい）3分の1だ。

Synonyms are おおむね, あらかた etc.

> 私は（×だいぶ／○だいたい／×大部分）いつも居間にいる。

  * **大部分**  
As you read, "(for) the great(est) part"; mostly noun, but also adverb. You
can use this word only for something whose percentage is clear rather than
subjective impression, and must tell "part of _what_ (noun)" (and conversely,
the other two are not going well with "of something").

> 彼女は人生の（×だいぶ／×だいたい／○大部分）を芸能界で過ごした。

