E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Nag.
A horse. This is an example of n of the article joined to the following noun, as in the word newt = an ewt. (Danish and Norwegian, og; Anglo-Saxon, eoh or eh; Latin, eq[uus]; Dutch, negge.) Taylor (1630) has naggon, as
1
Wert thou George with thy naggon,
That foughtest with the draggon.
Shakespeares naunt and nuncle are mine-aunt and mine-uncle.