What's the meaning of もの in this sentence?


> てっきり、兄{あに}は腰{こし}を下{お}ろす **もの** だと思{おも}っていた。

I have no clue about what it could mean.




> 「Phrase/Mini-Sentence + ものだと思っていた」

is probably better if you remembered it as a fixed expression meaning:

> "I just took it for granted that (Phrase/Mini-Sentence)."
>
> "I never had the slightest doubt that (Phrase/Mini-Sentence)."

It would be practically impossible to translate the 「もの」 all by itself here,
but it is being used to refer to an "assumed fact".

> 「てっきり、兄{あに}は腰{こし}を下{お}ろすものだと思{おも}っていた。」

therefore means:

> "Without thinking, I simply had assumed that my older brother would sit
> down."




> 「Phrase/Mini-Sentence + ものだと思っていた」

is probably better if you remembered it as a fixed expression meaning:

> "I just took it for granted that (Phrase/Mini-Sentence)."
>
> "I never had the slightest doubt that (Phrase/Mini-Sentence)."

It would be practically impossible to translate the 「もの」 all by itself here,
but it is being used to refer to an "assumed fact".

> 「てっきり、兄{あに}は腰{こし}を下{お}ろすものだと思{おも}っていた。」

therefore means:

> "Without thinking, I simply had assumed that my older brother would sit
> down."

