'ariya' defn.: ethically-noble different from enlightened-noble. In MN 4, Buddha was unenlightened at the time so he was ethically-noble

 From a conversation I had with 

Digital Pāḷi Dictionary

Team:

ariya 1	adj	noble; distinguished; of the Buddha
ariya 2	masc	ethically noble person; person of moral integrity
ariya 3	masc	awakened being; enlightened one; arahant
ariya 4	masc	name of a privately enlightened Buddha
ariya 5	masc	speaker of an Indo-Aryan language
ariya 6	adj	(abhidhamma) supra-mundane

Ariya 2

> So in MN 4 the Buddha (not enlightened then) was an ariya "being of integrity who is not enlightened" correct?

Yes

 I also checked the commentary which has 

tesamahaṃ aññataroti tesaṃ ahampi eko aññataro. bodhisatto hi gahaṭṭhopi pabbajitopi parisuddhakāyakammantova hoti.

I am one of them. Of them I too am one of them. Even a bodhisattva, even a householder, even a monk who has purified their physical conduct.

Ariya 5

is ariya 5 referring to the pre-buddhist meaning of ariya? 

Can any caste be ariya, in pre-buddhist meaning?

Ariya 6 gets used in Vinaya contexts when an Ariyan language speaker says something to a milakkhaka (barbarian, non-indo-aryan languge) and his words are not understood, the conditions for proper disrobing are not fulfilled. 

It is unrelated to caste, but to a person of a cultural language group. 

Yes the older meaning of arya. According to the latest genetic studies they entered India from modern day Turkmenistan about a millennia before the Buddha's time.