func·tion (fŭngkˈshən)

1. The physiological property or the special action of an organ or body part.
2. Something closely related to another thing and dependent on it for its existence, value, or significance, such as growth resulting from nutrition.
3. A mathematical variable so related to another that for each value assumed by one there is a value determined for the other.
4. A rule of correspondence between two sets such that there is a unique element in the second set assigned to each element in the first set.
5. The general properties of a substance, depending on its chemical character and relation to other substances, that provide the basis upon which it may be grouped as among acids or bases.
6. A particular reactive grouping in a molecule.