Just a reminder:
Going back to what "Ordinary" and "Extraordinary" mean in liturgical or ecclesiastical terms.
Ordo in Latin, has to to with putting things or people in an order. That is, organizing them according to a scheme.
Our trusty Lewis & Short Dictionary reminds us that the adjective ordinarius means "of or belonging to order, orderly; according to the usual order, usual, customary, regular, ordinary".
If we apply ordinarius to a person in the Church you wind up with the an "ordinary", the usual example of which is the local diocesan bishop (though others also are "ordinaries" too).
In a religious order, people live according to a rule.
Men who are ordained are in Holy Orders, so that they can help to put order into God’s people and live in a certain way.
When we get to the word "ordinary" in English but in Church terms, we shouldn’t automatically assume that something is of, for example, less quality or undeserving of attention. It means essentially that something is in the proper scheme of things. Consider "Ordinary Time" in the liturgical year. These Sundays are not unusual in the way that, say, Easter is out of the ordinary. In a sense, Easter is out of the ordinary because not every Sunday is Easter Sunday (yes, I know that some say every Sunday is a little Easter… but you get my point). In fact, Easter does come along regularly each year in the proper order of things. It is perfectly ordinary to find Easter at the conclusion of Lent and Holy Week. It is not rare.
On the other hand, Latin extraordinarius means, as you might expect "out of the common order, extraordinary". It is something that does not occur in the ordinary course. That does not mean that extraordinarius is therefore assumed to mean "rare". On the contrary, the idea of ordinarius seems to assume that there are regular interruptions because extraordinarie, the adverb, means in later Latin – for example in St. Jerome’s writing, "with excessive frequency". So, ordinarie suggests that there are regular deviations from a pattern, and that extraordinarie can be either something special or unexpected or a more than usual interruption of the regular order.
I don’t think it is fair to cast extraordinarius as simply "rare".
And I think we must exclude also the common British use of "extraordinary" in a negative sense or in the American usage for something remarkably good.