noun
Used as a noun meaning the absence of anything, often in philosophical, mathematical, or emphatic contexts. Common in set phrases like 無になる (come to nothing) or 無に帰す (return to nothing).
努力が無になった。
All my efforts came to nothing.
結果はゼロ、つまり無だった。
The result was zero, in other words, nothing.
prefix
Prefix that negates or indicates the absence of something. Attaches to nouns to form words like 無関心 (indifference), 無意味 (meaningless), 無条件 (unconditional). Productive but mainly in established compounds.
彼は政治に無関心だ。
He is indifferent to politics.
無意味な議論はやめよう。
Let's stop this meaningless argument.
The kanji 無 has been used in Chinese and Japanese to express negation or nothingness. The reading む is the on'yomi derived from Middle Chinese. The alternative form 无 is a historical variant.