As an accurate term to reflect much of contemporary Protestant thought it needs to be nuanced a bit, as your quoted definitions and those of 808bass have done.
Scripture is not the "only" thing used to form the Christian mind today, in this sense "sola" doesn't make sense.
Scripture is the ultimate (or primary) authority argued to. Authority of the local church, etc. exists but is secondary to that of Scripture. Does that qualify as "Sola"?
I think so. There are different levels of authority but as the primary Scripture stands alone. Sola. Scriptura.
SD
Don't you see, allend? No one can determine what Sola Scriptura means to anyone but himself. But Sola Scriptura itself does not mean that one determines the meaning of scripture strictly on the basis of personal interpretation.