WordNet (r) 3.0 (2006):

extrapolation
    n 1: (mathematics) calculation of the value of a function
         outside the range of known values
    2: an inference about the future (or about some hypothetical
       situation) based on known facts and observations

Moby Thesaurus II by Grady Ward, 1.0:

60 Moby Thesaurus words for "extrapolation":
   accession, accessory, accompaniment, actualization, addenda,
   addendum, additament, addition, additive, additory, additum,
   adjunct, adjuvant, annex, annexation, appanage, appendage,
   appendant, approximation, appurtenance, appurtenant, attachment,
   augment, augmentation, coda, complement, concomitant, continuation,
   corollary, differentiation, division, equation, evolution,
   extension, exteriorization, externalization, fixture, increase,
   increment, integration, interpolation, inversion, involution,
   multiplication, notation, objectification, offshoot, pendant,
   practice, projection, proportion, reduction, reinforcement,
   side effect, side issue, subtraction, supplement, tailpiece,
   transformation, undergirding



The Free On-line Dictionary of Computing (30 December 2018):

extrapolation
extrapolate
interpolation

    A mathematical procedure which
   estimates values of a function for certain desired inputs
   given values for known inputs.

   If the desired input is outside the range of the known values
   this is called extrapolation, if it is inside then it is
   called interpolation.

   The method works by fitting a "curve" (i.e. a function) to two
   or more given points and then applying this function to the
   required input.  Example uses are calculating trigonometric
   functions from tables and audio waveform sythesis.

   The simplest form of interpolation is where a function, f(x),
   is estimated by drawing a straight line ("linear
   interpolation") between the nearest given points on either
   side of the required input value:

   	f(x) ~ f(x1) + (f(x2) - f(x1))(x-x1)/(x2 - x1)

   There are many variations using more than two points or higher
   degree polynomial functions.  The technique can also be
   extended to functions of more than one input.

   (2007-06-29)