(Oxford English Dictionary)
[ad. Du. baas master (older sense 'uncle'), supposed to be related to Ger. base female cousin, OHG. basa 'aunt'.]
An orig. American equivalent of 'master' in the sense of employer of labour; applied also to a business manager, or any one who has a right to give orders. In England at first only in workmen's slang, or humorously, = 'leading man, swell, top-sawyer'; now in general use in Britain.
[a1649 J. WINTHROP Hist. New England (1908) I. 166 Here arrived a small Norsey bark..with one Gardiner, an expert engineer or work base [= Du. werk-baas], and provisions. 1653 F. NEWMAN et al. Let. May in E. Hazard Hist. Collections (1794) II. 236 From our Place of Residence at the Basses house in the Monhatoes.]
1806 W. IRVING Let. 26 May in P. M. Irving Life & Lett. (1862) I. xi. 138, I had to return, make an awkward apology to boss, and look like a nincompoop. 1813 LD. YARMOUTH Let. 12 Dec. in E. Taylor Taylor Papers (1913) vii. 98 There are some peasants watching, one of whom has frightened the boss with an alarm of a sortie.