All 3 Uses

function
in
Here, There be Dragons by Owen
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I have a basic functional knowledge of several languages, but know almost nothing of the rest of them.†
Chpt 2.8 *
"Those toys were not meant to engage in debate, much less function indefinitely," he said, "just to keep a semblance of order until I could assume my place on the Silver Throne.†
Chpt 3.9
He couldn't quite bring himself to admit all that had gone wrong in the Archipelago: the inability to function as a translator, followed by the actual loss of the Geographica itself.†
Chpt 4.14 *

Definitions:

(1) (function as in: Its main function is to...)
purpose, job, or natural activity
(2) (function as in: can't function well without sleep)
work or operate -- sometimes to work or operate normally or in a particular way
(3) (function as in: I'm attending a function tonight)
a social event or ceremony -- especially one attended for work or out of a sense of duty
(4) (function as in: oxygen is a function of altitude)
saying one results from another; or saying that the amount of one thing is dependent upon the value of another.

If x is a function of y, then x results from y; or the amount of x can be calculated based on the amount of y.
(5) (function as in: Amazon's new search function)
computer code that performs a specific task
(6) (function as in: a mathematical function)
a formula or mathematical expression that describes a relationship between variables
(7) (meaning too rare to warrant focus)
For more specialized meanings in math and chemistry, see a comprehensive dictionary.