noun
what kind of thing; what
Used to ask about the nature or identity of something, often with a nuance of suspicion or emphasis. Common in rhetorical questions.
これは一体何物だ？
What on earth is this?
彼は何物にも代えがたい存在だ。
He is irreplaceable (lit. something that cannot be exchanged for anything).
noun
anything (else); nothing (but)
Used in negative or limiting constructions such as 何物にも, 何物でもない, meaning 'nothing but' or 'anything else'. Often emphasizes exclusivity or negation.
彼は何物にも動じない。
He is unfazed by anything.
それは何物でもない。
That is nothing (of significance).
Compound of 何 (nani, 'what') + 物 (mono, 'thing'). The reading なにもの is a straightforward combination of the two components.