Donkey is a word of late appearance and of uncertain origin.
It was first defined by the English antiquary and lexicographer Francis Grose (1731-91) in A Classical Dictionary of the Vulgar Tongue (1785):
Donkey, donkey dick: a he, or jack ass, called donkey, perhaps from the Spanish or don-like gravity of that animal, entitled also the king of Spain’s trumpeter.
In his Memoirs, the English lawyer William Hickey (1749-1830) described his sojourn in Lisbon in 1782:
We also went upon parties formed by Mrs Walpole or Mrs Warden to the different Royal palaces and principal noblemen’s castles, especially those of Cintra and other beautiful spots within twenty miles of the capital, these excursions being made in carriages, on horseback, and donkeys (asses), the latter animals being exclusively for the ladies’ use.
These memoirs were composed in 1808-10, but the author still felt the need to explain the word donkey.
The etymology given by Francis Grose is fanciful. However, the reference to the word don, in the sense of a Spanish title, is interesting. This Spanish word derives from Latin dominus, meaning lord, master, and in The Nun’s Priest’ Tale the English poet Geoffrey Chaucer (circa 1342-1400) called the ass Dan Burnel, that is, Master Brown. (In the same tale, the fox is called Dan Russell, that is, Master Red.)
It is therefore possible that the word donkey originally referred to the colour of its pelage: it might derive from the adjective dun, which denotes of a dull greyish-brown colour. Similarly, dunnock, which designates the hedge-sparrow, is apparently composed of dun and the diminutive suffix -ock, from the dusky brown colour of its plumage.
However, donkey has more probably a different origin. Other colloquial appellations of the ass include:
– neddy, which is a diminutive of Ned, pet form of the given name Edward
– dicky, a diminutive of Dick, pet form of Richard
– cuddy, a Scottish appellation which is probably a diminutive of Cuthbert. Like donkey, this word only appeared in the 18th century.
(Likewise, hobby, which originally denoted a small horse, is a diminutive of Hob, pet form of Robert.)
The word donkey might therefore derive from a given name, perhaps Duncan or Dominic.
This origin seems to be supported by the following from A List of Local Expressions published in The Gentleman’s Magazine and Historical Chronicle of December 1793:
A Donky, or a Dicky: an ass. Essex and Suffolk. The colliers of Kingswood call the same animal a Neddy-ass, but more usually a Neddy.
Anna Lætitia Barbauld (1743-1825) was an English poet, essayist, literary critic, editor and children’s author. In a letter dated 11th August 1804, she described to a Miss Susan Taylor of Norwich her visit to Tunbridge Wells:
O that you were here, Susan, to exhibit upon a ‘donky’,―I cannot tell whether my orthography is right, but a donky is the monture in high fashion here; and I assure you, when covered with blue housings, and sleek, it makes no bad figure:—I mean a lady, if an elegant woman, makes no bad figure upon it, with a little boy or girl behind, who carries a switch, meant to admonish the animal from time to time that he is hired to walk on, and not to stand still. The ass is much better adapted than the horse to show off a lady; for this reason, which perhaps may not have occurred to you, that her beauty is not so likely to be eclipsed: for you must know that many philosophers, amongst whom is ———, are decidedly of opinion that a fine horse is a much handsomer animal than a fine woman; but I have not yet heard such a preference asserted in favour of the ass,―not our English asses at least,―a fine Spanish one, or a zebra, perhaps…