ap·prox·i·mate • adj. / əˈpräksəmit/ close to the actual, but not completely accurate or exact: the calculations are very approximate.• v. / -ˌmāt/ [intr.] come close or be similar to something in quality, nature, or quantity: a leasing agreement approximating to ownership | [tr.] reality can be approximated by computational techniques. ∎  [tr.] estimate or calculate (a quantity) fairly accurately: I approximated the horse's weight.DERIVATIVES: ap·prox·i·mate·ly adv.ap·prox·i·ma·tion / əˌpräksəˈmāshən/ n.

approximate very near in position or nature XV; nearly exact XIX. — late L. approximātus, pp. of approximāre, f. AP- + proximus PROXIMATE.
Hence, or directly f. pp. stem approximāt-, approximate vb., approximation XV.