The Oxford Thesaurus An A-Z Dictionary of Synonyms - extension n.

1) stretching, expansion, increase, enlargement, augmentation, development, amplification, broadening, widening, lengthening, spread, spreading: The extension of the plan is scheduled for next year. 2) range, extensiveness, scope, extent, magnitude, gauge, compass, sweep, reach, size, volume, dimension(s) , proportions, capacity, span; breadth, width, height, length, spread, stretch: The extension of the mind seems almost limitless. 3) addendum, addition, annexe, wing, adjunct, ell, appendage; appendix, supplement: We have built an extension to the house.