«أَوْ تَضَايُفٌ»
Or a reciprocal relational connection.
Pairs such as father and son or cause and effect are conceived through mutual reference: fatherhood is relative to a child, and an effect is understood in relation to a cause.
This is an intelligible conceptual relation, hence a rational link. A pair of words often mentioned together in ordinary conversation is not automatically an instance of technical correlation.