yenavrta ime lokas
sa vai vrtra iti proktah
yena—by whom; avrtah—covered; ime—all these; lokah—planets; tapasa—by the austerity; tvastra-murtina—in the form of the son of Tvasta; sah—he; vai—indeed; vrtrah—Vrtra; iti—thus; proktah—called; papah—personified sin; parama-darunah—very fearful.
That very fearful demon, who was actually the son of Tvasta, covered all the planetary systems by dint of austerity. Therefore he was named Vrtra, or one who covers everything.
In the Vedas it is said, sa imal lokan avrnot tad vrtrasya vrtratvam: because the demon covered all the planetary systems, his name was Vrtrasura.
Link to this page: https://prabhupadabooks.com/sb/6/9/18