In a previous post, I had noted that Q was used as an abbreviation for Quelle in pre-1880 geography books, and suggested this as a longshot hypothetical background to the adoption of the siglum in NT studies. Perhaps something more relevant came to my attention today, even if it is nearly as speculative. In reading John Rogerson’s learned book on the development of Old Testament scholarship in England and Germany in the 19th century, I was struck by the fact that Wellhausen used ‘Q’ as a siglum for a hypothetical source of the Pentateuch in an 1876 article on ‘Die Composition des Hexateuchs,” in the Jahrbuch für Deutsche Theologie – although Wellhausen used it as an abbreviation for ‘quatuor’ rather than for Quelle. He writes, “Ich habe für die s.g. Grundschrift das Zeichen Q gewählt, als Abkürzung für Vierbundesbuch (quatuor), welchen Namen ich als den passendsten für sie vorschlage” (392: ‘I have chosen the siglum Q as an abbreviation for the so-called Grundschrift, which stands for the ‘four-covenant book’ (quatuor) which name I propose as the most appropriate for it’).
Admittedly it’s not exact, but might this have primed the NT world to think of Q as standing for a hypothetical biblical source behind the canonical accounts? Pure speculation, but a strikingly analogous designation and function.