अर्यः स्वमि-वैश्ययोः

The word अर्य is irregularly formed when meaning 'lord' and a 'Vaisya'.
The root ऋ 'to go', would have taken ण्यत् by sutra 124 of this chapter; but it takes यत् when the sense of the word formed by it is that of a 'lord' or a man of 'Vaisya' caste. As अर्यः स्वामी, 'honored lord', अर्ये वैश्यः 'honored Vaisya'.

Vart: Though by (VI. I. 213), the affix यत् makes the udatta accent fall on the first syllable of the word, yet in the case of the word अर्य, when it means 'lord', the accent falls on the last syllable.

Why do we say 'when it means a lord or a Vaisya'? Otherwise the root takes the affix ण्यत्; as आर्यो ब्राह्मणः 'the respectable Brahmana'.,