in no uncertain terms

in a way that is most clear or direct

The exact origin of the phrase "in no uncertain terms" is not well-documented, but it has been in use for well over a century. It likely evolved from the notion that clear and direct language leaves no room for doubt or misunderstanding, emphasizing the absence of uncertainty. It is used to emphasize that something is stated clearly, directly, and without any ambiguity or room for misinterpretation.

She was told in no uncertain terms that the magazine had no interest in her short stories.
She told him in no uncertain terms that his behavior was unacceptable and needed to change immediately.
The boss informed the team in no uncertain terms that the project's success was crucial and required their full dedication.
When discussing their expectations for the new employee, the manager outlined the job requirements in no uncertain terms.
The warning was issued in no uncertain terms, alerting residents to evacuate due to the approaching hurricane.