to insert (something) between other things or parts, esp to insert (words) into a text or conversation
to alter or corrupt (e.g. a text) by inserting new, false, or misleading matter
in mathematics, to estimate values of (a function) between two known values
interpolation /-ʹlaysh(ə)n/ noun
interpolative /-lətiv/ adj
interpolator noun
[Latin interpolatus, past part. of interpolare to refurbish, alter, interpolate]