What does Rishi mean?
From the Sanskrit ऋषि (ṛṣi), 'a seer, sage, inspired poet' — the title of the sages to whom the Vedic hymns were revealed. A firmly established classical word.
What does Aarush mean?
From Sanskrit arusha (आरुष), 'reddish, red of dawn', commonly glossed as 'the first ray of the sun'. The 'red/dawn' sense is the attested one; 'first ray of sun' is the popular reading.