A long time ago, I was solving this puzzle and got stuck at an unguessable (to me) crossing: N. C. WYETH crossing NATICK at the "N"—I knew WYETH but forgot his initials, and NATICK ... is a suburb of Boston that I had no hope of knowing. It was clued as someplace the Boston Marathon runs through (???). Anyway, NATICK— the more obscure name in that crossing—became shorthand for an unguessable cross, esp. where the cross involves two proper nouns, neither of which is exceedingly well known. NATICK took hold as crossword slang, and the term can now be both noun ("I had a NATICK in the SW corner...") or verb ("I got NATICKED by 50A / 34D!")