known quantity
noun phraseUK /nəʊn ˈkwɒntəti/
US /noʊn ˈkwɑːntəti/
A known quantity is a person or thing that you already know well and can trust.
After working with her for years, the manager considered her a known quantity.
RELATED WORDS
OTHER MEANINGS
2. A number or amount that is already known in a math problem.
In the equation, x is the unknown and 5 is the known quantity.
3. Something whose value or quality is already established.
The old car was a known quantity, so the buyer felt safe purchasing it.
4. A person whose abilities and behavior are already understood by others.
The new coach was a known quantity in the league, which made hiring him easy.