noun
Literal meaning: a single item or object. Often used in set phrases like 一物もない (not a single thing).
机の上には一物もなかった。
There was not a single thing on the desk.
noun
ulterior motive; secret intention; plot
Implies a hidden agenda or scheme behind someone's actions. Often used in the phrase 一物がある (to have an ulterior motive).
There must be an ulterior motive behind his sudden kindness.
あの提案には一物ありそうだ。
That proposal seems to have a hidden agenda.
noun
Euphemistic slang for the male genitalia. Usually written in katakana as イチモツ. Not used in formal contexts.
彼はイチモツの話ばかりする。
He always talks about his junk.
noun
Rare euphemism for money, possibly from the idea of 'one valuable thing'. Not common in modern speech.
昔の小説では、一物を「金」の婉曲表現として使うことがある。
In old novels, 一物 is sometimes used as a euphemism for money.
Literally 'one thing'. The sense of 'ulterior motive' likely developed from the idea of having 'one thing' hidden behind one's actions. The euphemistic uses are slang extensions.