According to Wikipedia Q source is sometimes called the Q Gospel. My understanding of Q though is that it is proposed mostly as a collection of sayings. Is it proper to call it a "Gospel"? Why or why not?
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The Gospel of Thomas consists mostly of sayings, and it explicitly claims to be a Gospel in its first sentence. So that's pretty good evidence that something like Q would have been thought of as a gospel around the time when Thomas was written (which is sometime between the mid 1st and mid 2nd century, we don't know).
On the other hand, we don't know when "gospel" was first used as a name of a genre or writing. One theory is that it was first used to refer to a genre of writing in Mark 1:1. So it might be anachronistic to refer to Q as a gospel, since the genre may not have yet existed.
To me, in order for any book to be considered a Gospel the first thing it would have to have is the teaching of the death, burial, and resurrection of Jesus Christ since that's what the word means in the underlying NT Greek in the canonical Gospels. That is the good news after all; that Christ died, was buried, and rose again!