Definition of "hummum"

a curious summer-house, excelling all his other for prospect, painting, hummum, waterworks, and a forest which is stored with game of several sorts

1634, T[homas] H[erbert], A Relation of Some Yeares Trauaile, Begunne Anno 1626. into Afrique and the Greater Asia, […], London: […] William Stansby, and Jacob Bloome

Of all those knights and baronets, lords and gentlemen, bearing arms, whose escutcheons are painted upon the walls of the famous hall of the Upper Temple, was there no philanthropist good-natured enough to devise a set of Hummums for the benefit of the lawyers, his fellows and successors?

1848 November – 1850 December, William Makepeace Thackeray, chapter 30, in The History of Pendennis. […], volumes (please specify |volume=I or II), London: Bradbury and Evans, […], published 1849–1850