NOUN (2)

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