Slughorn can refer to several things and one (fictional) person.
The Oxford English Dictionary, second edition, prepared by J. A. Simpson and E. S. C. Weiner, vol. xv, Ser-Soosy, under "slogan" and "slughorn (1)".
Thomas Chatterton, The Rowley Poems, Hastings ii.90 and footnote 15 to Eclogue the Second, at Project Gutenberg, accessed on 12 July 2006.
Robert Browning, Browning's Shorter Poems, selected and edited by Franklin T. Baker, A.M., Macmillan, 1917 at Project Gutenberg, accessed on 12 July 2006.