What is the meaning of もの in that sentence 真相を知るものは誰もいません
Dictionary says it can mean 'thing', but also 'really'.
I guess thus it's 'really' but when I automatically translate this sentence, the meaning 'really' never appears.
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Sign up to join this communityもの has a variety of uses. While it can mean thing, it can also refer to a person, which is what it's doing in this sentence.
Breaking the sentence down, we have:
真相を知る: <someone> knows the truth.
誰もいません: There is no one.
もの is the glue that ties these two parts together.
First note that, when 真相を知る is placed before もの, it's acting as a relative clause. So,
真相を知るもの: someone who knows the truth
And so when placed in the larger sentence,
真相を知るものは誰もいません: There is no one who knows the truth.