known quantity

noun

1. Mathematics.,  a quantity whose value is given: in algebra, frequently represented by a letter from the first part of the alphabet, as a, b, or c.

2. any factor, circumstance, etc., that is already accepted or familiar.

   Her honesty is a known quantity.

Word History and Origins

Origin of known quantity¹

First recorded in 1975–80

Example Sentences

In each case, Riley has opted to keep the known quantity.

Read more on Los Angeles Times

Now a known quantity, Saints reduced their kicking to Caluori to deal with the breakout star's freakish aerial ability, while the teenager struggled to get the ball in hand to show his running power.

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Still, with some unknowns in the Chargers’ receiving corps outside of Ladd McConkey and Quentin Johnston, it makes sense that they would want to bolster their passing game with a more known quantity in a player such as Allen.

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He is, in other words, a known quantity.

Read more on Slate

As opposed to the much more “easy reader” version, which is bringing the same sensibility to the same music and feeling stuck but giving your fans a known quantity they can eat and consume year in and year out.

Read more on Salon