The meanings of old words are often layered, and so it is with a very old Hebrew word, "olam." However people understood it while including it in a brakhah, it now carries with it all the meanings it has ever held.
We usually see it translated as "universe" (as in "...King of the universe"). In the Bible, olam carries the meaning of the physical world in its totality. Of course, the physical world was presumed to be much smaller back then, but even today when we speak of the World, we mostly mean this globe called Earth. Describing God as "melekh ha'olam" means God has full dominion over the world we encounter with our five senses.
By rabbinic times, the word had come to mean the realm of time. We encounter it in phrases like "l'olam va'ed" (to the end of time and beyond), the Aramaic version "l'alam u'l'olmei olmaya" (forever and forever and ever), and "olam hazeh" and "olam haba" (human history and the afterlife). In this context, God rules all of time, forever.
Olam also carries the root of the word for "disappear" (that is, to become part of everything else), and for a young man or woman (someone on the verge of full adulthood).
That more poetic meaning and the images it provokes are present in the common translation of "universe." It means "one direction," even if we use it to mean all of the cosmos. But we also speak of a universe of discourse (common ground for understanding), universal health care coverage (equally accessible to all), Universal Studios (a name certainly chosen to convey grandiosity). Moreover, we hear that same poetry in the word "verse," which resonates in poem and song.
To describe God as "melekh ha'olam" is to acknowledge that there is no realm that escapes God's authority – not time, not space and not even our own creative imaginations. When we seek to hide, it is not a pleasant thought. But when we seek to pray, it is comfort and encouragement.
So now we have completed the formula "Barukh ata adonai eloheinu melekh ha'olam; Empowered are You, my Compassionate One, our Judge, ultimate authority over all of existence…" How does one follow an act like that?