From Byron's *[Don Juan](https://en.wikisource.org/wiki/Don_Juan_(Byron)/Canto_the_Sixth)*:

> 
> One with her flush'd cheek laid on her white arm,  
> 
>  And raven ringlets gather'd in dark crowd  
> 
>  Above her brow, lay dreaming soft and warm;  
> 
>  And smiling through her dream, as through a cloud  
> 
>  The moon breaks, half unveil'd each further charm,  
> 
>  As, slightly stirring in her snowy shroud,  
> 
>  Her beauties seized the unconscious hour of night  
> 
>  All bashfully to struggle into light. 
> 
> 
> This is no **bull**, although it sounds so; for  
> 
>  'T was night, but there were lamps, as hath been said.  
> 
>  A third's all pallid aspect offer'd more  
> 
>  The traits of sleeping sorrow, and betray'd  
> 
>  Through the heaved breast the dream of some far shore  
> 
>  Belovéd and deplored; while slowly stray'd  
> 
>  (As night-dew, on a cypress glittering, tinges  
> 
>  The black bough) tear-drops through her eyes' dark fringes.
> 
> 
> 

I immediately thought that this meant **bullshit**, but then I consulted dictionaries and discovered that **bullshit** was coined in the 20th century. Yet it clearly means "false information" here. 

If not from **bullshit**, what does it derive from?