Interpolate
Etymology
From Latin “interpolare,” to touch up or refurbish, from “inter-” (between) and “polire,” to polish. Its early English meaning was damning: to interpolate a manuscript was to tamper with it by inserting spurious passages. The neutral mathematical sense — estimating between known values — came later, but the whiff of insertion remains.
verb · /in-TER-puh-layt/
To insert an estimated value between two known ones, or to insert new matter into an existing text.
What it names
Filling a gap between fixed points — and, in its older sense, the quieter act of slipping material into something already written.
Example
Where the ancient census was missing years, historians interpolate the population from the surrounding decades.
Related idea
To interpolate is to fill in between the known; to extrapolate is to push beyond it. The first is bounded on both sides; the second is a leap into open air.
See also