A function indicates a relationship in prospect, and so
belongs to a family of concepts. Relationship, as in related;
relationship, as in connected,
corresponding to or caused by,
united or bound together;
relationship, as in linked or yoked,
coupled or conjoined,
associated or allied.
Relationship, as in dependent, indeed,
relationship, as in function of,
at which point the moving conceptual point may be seen revolving around the perimeter of a circle.
from 'A Tour of the Calculus', by David Berlinski (Bold print has been added.)