Real Dictionary

function
If you say that one thing is a function of another, you mean that its amount or nature depends on the other thing.
the division of a physical or abstract whole into its constituent parts to examine or determine their relationship or value [...]
the natural action or intended purpose of a person or thing in a specific role [...]
countable noun: A function is a large formal dinner or party.
countable noun: A function is a series of operations that a computer performs, for example when a single key or a combination of keys is pressed.
countable noun: The function of something or someone is the useful thing that they do or are intended to do.
verb: If a machine or system is functioning, it is working or operating.
verb: If someone or something functions as a particular thing, they do the work or fulfil the purpose of that thing.