What does Ishan mean?
From the Sanskrit ईशान (īśāna), 'ruler, master'. It is an epithet of the god Shiva, also denotes the sun and the north-eastern quarter (one of the dikpalas). A genuine, well-attested Vedic/classical term.
What does Om mean?
From Sanskrit Om (ॐ), the sacred primordial sound and mantra regarded in Hindu tradition as the essence of the universe. Used as a name it carries that whole spiritual weight.