Interest (finance)
Etymology
From Latin "interest" (it matters, it makes a difference), from "interesse" — inter "between" + esse "to be". Medieval lawyers used "interesse" for compensation owed for a lender’s loss, a workaround for the Church’s ban on "usury": the charge was framed not as profit on the loan but as the "difference" the money would have made.
noun · /IN-truhst/
The cost of borrowing money, or the reward for lending it, usually charged as a percentage over time.
What it names
The single most important number in personal finance — the price of time on money, working for you when you save and against you when you owe.
Example
At 24% interest, the unpaid card balance nearly doubled his original purchase within four years.
Related idea
Distinguish usury, which named any interest at all in medieval usage but now means only interest charged at illegally or unethically high rates.
noun · /IN-truhst/
A legal or financial stake, share, or claim in something — as in a controlling interest in a company.
What it names
Ownership and skin in the game rather than the cost of borrowing, and underlies phrases like ‘conflict of interest’ and ‘vested interest.’
Example
She holds a majority interest in the family firm.
Related idea
This is the sense behind a conflict of interest and a stakeholder's claim — ownership and skin in the game, not the price of borrowing money.
noun · /IN-truhst/
The feeling of wanting to know about or engage with something, or the quality in a thing that draws such attention.
What it names
Both the pull you feel toward a subject and the power a thing has to create that pull (‘a book of great interest’).
Example
Her interest in astronomy started with a backyard telescope.
Related idea
Curiosity is the active urge to find something out; interest is broader and steadier — a sustained engagement or appeal that can simmer without any burning question.
noun · /IN-truhst/
A person’s benefit or advantage — what is good for them, as in ‘your best interest.’
What it names
A party’s welfare: the outcomes that help or harm them, as weighed in ‘conflict of interest’ or ‘the public interest.’
Example
It is in your interest to read the contract before signing.
Related idea
This shades into the legal ‘stake’ sense but is broader and less formal — not a measurable share you own, but simply what serves your good.