1. To cause something to gush or discharge upward suddenly and with great force or volume. In this usage, a noun or pronoun can be used between "spew" and "up." The volcano has been spewing up plumes of ash and toxic gas for days now. The broken water main spewed water up ten feet into the air.

2. slang To vomit (something), especially at great length, with great force, or in great volume. In this usage, a noun or pronoun can be used between "spew" and "up." I thought he was going to spew up, so I pulled the car over and let him out onto the curb. I got so drunk that I ended up spewing my dinner up onto the bar.