Real Dictionary

diminishing returns
uncountable noun: In economics, diminishing returns is a situation in which the increase in production, profits, or benefits resulting from something is less than the money or energy that is invested.

diminishing returns in American English
the proportionately smaller increase in productivity observed after a certain point in the increase of capital, labor, etc.
noun: any rate of profit, production, benefits, etc., that beyond a certain point fails to increase proportionately with added investment, effort, or skill

diminishing returns in British English
plural noun: progressively smaller rises in output resulting from the increased application of a variable input, such as labour, to a fixed quantity, as of capital or land

diminishing returns in Finance
noun: Diminishing returns is a situation in which production, profits, or benefits increase less and less as more money is spent or more effort is made.