There are words which in technical terminology have a definite meaning, but in the everyday universe of human lives, are highly subjective. For example, if you make a decision based on a gut instinct, is it rational?
We usually think of a rational decision to be based on logic. A gut instinct is not consciously based on logic, so it is not consciously rational by that definition. However, when you look closer you generally find that a gut instinct is actually based on information acquired from a variety of sources, added together in a logical way. That makes it rational by that definition.
Furthermore, if a person has a good ability to make instinctive judgments and those serve them well over the course of a lifetime, they might come to depend on them. That is a rational choice, because it makes logical sense to do things using a tried and true method.
Ultimately, everything is rational. However there are scales of increasing complexity that come into play, and there are parts of the mental processes that shuttle around extremely high information densities. It’s unsurprising that we don’t always percieve our thoughts as being rational. But every instinct that is programmed into us has a good logical purpose once you understand it.
