[eli]

Hm, I'd assumed that was a reference to the newspaper/typesetting term "slugline". But maybe it's both.

[ghaff]

I'm not sure the "slugline" term is common for that meaning; it's typically (don't know how widely it's still used) just slug. But it's a pretty obvious and clever derived term to combine slug and headline and come up with slugline.

Slug line (two words) is apparently a screenwriting term--which I didn't know.

[eli]

I don't think slugline was derived from headline. On old linotype machines, the slug was literally a line of metal.

[rhino369]

That might be it actually.