approximation

n. approach; estimate, guess, conjecture

An approximation is an inexact representation of something that is still close enough to be useful. Although approximation is most often applied to numbers, it is also frequently applied to such things as mathematical functions, shapes, and physical laws.Approximations may be used because incomplete information prevents use of exact representations. Many problems in physics are either too complex to solve analytically, or impossible to solve. Thus, even when the exact representation is known, an approximation may yield a sufficiently accurate solution while reducing the complexity of the problem significantly.
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Noun
1. an approximate calculation of quantity or degree or worth; "an estimate of what it would cost"; "a rough idea how long it would take"
(synonym) estimate, estimation, idea
(hypernym) calculation, computation, figuring, reckoning
(hyponym) guess, guesswork, guessing, shot, dead reckoning
2. the quality of coming near to identity (especially close in quantity)
(hypernym) similarity
3. an imprecise or incomplete account; "newspapers gave only an approximation of the actual events"
(hypernym) version
4. the act of bringing near or bringing together especially the cut edges of tissue
(synonym) bringing close together
(hypernym) joining, connection, connexion

n. approximation, approach

(n.)
The act of approximating; a drawing, advancing or being near; approach; also, the result of approximating.
  

(n.)
An approach to a correct estimate, calculation, or conception, or to a given quantity, quality, etc.
  

(n.)
A value that is nearly but not exactly correct.
  

(n.)
A continual approach or coming nearer to a result; as, to solve an equation by approximation.