moonman, n. — Green’s Dictionary of Slang

moonman n.

also moon’s man

[‘A moon-man signifies in English a madman...But these moon-men...are neither absolutely mad, nor yet perfectly in their wits. Their name they borrow from the moon, because, as the moon is never in one shape two nights together, but wanders up and down Heaven like an antic, so these changeable-stuff-companions never tarry one day in a place...’ Dekker (1608); this discussion of England’s gypsies is the first ever to be printed]

a gypsy.

1608		Dekker Lanthorne and Candle-Light Ch. 8: They are a people more scattred then lewes, and more hated: beggerly in apparell, barbarous in condition, beastly in behauior: and bloudy if they meete aduantage. A man that sees them would sweare they had all the yellow Iawndis, or that they were Tawny Moores bastardes, for no Red-oaker man caries a face of a more filthy in complexion; yet are they not borne so, neither has the Sunne burnt them so, but they are painted so: yet they are not good painters neither, for they do not make faces, but marre faces. By a by-name they are called Gipsies, they call themselues Egiptians, others in mockery call them Moone-men.
1621		Jonson Gypsies Metamorphosed 28: town: Game They are Gipsies of this yeare o’ this Moone in my Conscience. clod: O they are Calld the Moone men I remember now.
c.1698		B.E. Dict. Canting Crew n.p.: Moon-men c. Gipsies.
1725		New Canting Dict. [as cit. c.1698].
1737, 1759, 1760, 1776		Bailey Universal Etym. Eng. Dict. [as cit. c.1698].
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue.
1811		Lex. Balatronicum.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.