1. To become visible by or as by rising up from some point or source. The huge, imposing monument loomed up as we drove toward the city. A huge hooded figure loomed up from the shadows, wielding a knife and demanding that we give him our wallets.
2. To become nearer in time, causing dread or anxiety in the process. With the deadline looming up, I grew more and more panicked about what I was going to write.
3. To become more definite or probable, typically in a threatening way. With a government shutdown looming up, congress scrambled to pass a budget that satisfied both political parties' demands.
to appear to rise up [from somewhere]; to take form or definition, usually threatening to some degree. A great city loomed up in the distance. It looked threatening in the dusky light. A ghost loomed up, but we paid no attention, since it had to be a joke. The recession loomed up, and the stock market reacted.