Green’s Dictionary of Slang

1. a boaster.

1568		Hist. of Jacob and Esau V vi: What ye saucie merchaunt, are ye a prater now?
1664		C. Cotton Virgil Travestie (1765) Bk I 28: And as thou art a cunning Prater, / Play me the fine Insinuator.
1756		W. Toldervy Hist. of the Two Orphans IV 91: Thus this prater begins, pray hear Humphry Copper!
1772		G. Stevens ‘Not As It Shou’d Be’ in Songs Comic and Satyrical 118: How many loud Coffee-house praters / Will boast of the weight / Which they have in the State. [Ibid.] ‘The Specific’ 162: Wine [...] At once turns a Mute to a Prater.

2. an itinerant, bogus preacher.

1674		Rochester ‘Tunbridge Wells’ in Works (1999) 49: I Trotted to the waters, / The Rendezvous of fools, Buffoons, and Praters.
1886		W. Newton Secrets of Tramp Life Revealed 22: We will now have a word with the tramp parsons. These travel in fours and fives. The head man calls himself the ‘Prater,’ or preacher. Their only object is to make money.