The French masculine noun sanglier denotes a full-grown wild boar. It literally means a boar living on its own, separated from the herd, since, via Old and Middle French forms such as sengler and senglier, it is from the popular Latin singularis (porcus), solitary (pig) – cf. Middle-French terms such as porc sanglier, and in the Vulgate, the Latin version of the Bible, singularis ferus, the noun ferus meaning wild animal (cf. the English adjective feral).

French sanglier is therefore a doublet of the noun and adjective singulier, meaning singular.

Since around 1400, English has used the French animal name in forms such as synglere, singuler and sanglier. For example, in The noble arte of venerie or hunting (1575), the English soldier and poet George Gascoigne (died 1577) wrote the following in the chapter titled The termes of the Ages of all beasts of Venerie and Chace:

A Bore is the first yeare a Pigge, the second an Hogge, the third a Hogsteare, the fourth a Bore, and the fifth yeare a Singuler, or (as I would thinke more properly spoken) a Sanglier, according to the French worde.

In Dictionnaire Œconomique; or, The Family Dictionary (1725), an adaptation of the second edition (1718) of the encyclopaedia compiled by the French agronomist Noël Chomel (1633-1712), the English botanist Richard Bradley (1688?-1732) wrote:

WILD-BOAR, a Wild-Hog, that is generally of a Black colour, or some other inclining to it, he has a furious Eye, and large, sharp and cutting Tushes: He is call’d a Pig of the Sounder the first, a Hog the second, and a Hog-Steer the third Year of his Age; but when he comes to the fourth Year he is call’d a Hog, and leaves the Sounder: He is also call’d Singlet or Sangler; this Animal is always Pigg’d with as many Teeth, as he shall ever have after, which will only increase in Bigness, but not in Number; amongst which he has four, which are call’d Tushes or Tusks, whereof the two Biggest do not hurt when he strikes, but serve only to whet the other two lowest, with which they frequently Kill: When they fight against one another, and see a Wolf coming, they lay aside their Quarrel, and join together to defend themselves; they go in Herds, and suffer no other Animal, that is not of their kind, to Herd with them.
They Feed upon all kind of Corn and Fruit which they can come at, also upon Roots, and in April and May, upon the Buds of Plum-Trees and Chesnut-Trees [sic], and all other sweet Buds they can find, and are never Measled as our tame Swine: Their Season begins in the midst of September, and ends about the beginning of December, when they go a Brimming.
Those Parts of this Animal which are used in Physick, are his Grease or Fat, his Testicles, his Gall, Ordure and Urine.
His Grease is very singular to allay Pains in the Side, and to mollify the Matter: Some hold that if it be drank in some Wine or Vinegar, it will stop the Spitting of Blood; and that if it be mix’d with Oil of Roses, it’s a good Remedy for Dislocations.
The Testicles are good to invigorate the Body, and to help the work of Generation.
The Gall is used for the cure of the Evil, and for the Stone or Gravel.
The Dung being dry’d and drank in a proper Liquor, or apply’d outwardly, will stop the Spitting of Blood.
The Urine of the Wild-Boar has several Vertues: You must take his Bladder, in which some store of Urine remains, and with this Urine mix a small Matter of Oil; then hang up the Bladder, so as to receive the Smoak of the Chimney, and leave it till the Urine thickens and is come to the consistence of Honey; and then keep it carefully in its Bladder, and therewith rub the Navels and Noses of young Children, that are troubled with Worms: This has been found to be attended with much Success several times; the Urine thus prepar’d, will break the Stone in the Bladder, particularly if you Drink a little of it.
The flesh of a Wild-Boar is better than that of a Deer; and we may appeal to the magnificent Feasts of the Romans, who so much valued this Flesh, that Wild-Boars were serv’d in whole to their Tables; the great Men of our Time value it much; especially Wild-Boars Head, is reckon’d to be exquisite and delicious Food, and the young ones are much valued in the Winter Feasts and Banquets; It’s certain that the Flesh of a Wild-Boar, yields much Nourishment, and breeds a deal of good Blood; and this is the reason that Physicians value it so much, and especially that of a Wild-Boar which has been Hunted down.
To Dress a Boars-Head for an Intermess; let it first be well sing’d at a clear Fire, and rubb’d with a piece of Brick to take off the Hair, let it also be scraped with a Knife and well cleansed; after you have bon’d it, cut out the two Jaw Bones, and the Snout, slit it underneath, in such a manner that it may stick to its skin on the top, and take away the Brain and Tongue: Then take up some Salt with the point of your Knife, and cause it to penetrate thro’ all the Parts of the Flesh: Afterwards let the whole Head be set together again, and well tied up, wrapping it in a Napkin; in the mean while get a great Kettle [= cauldron] almost full of Water, hang it over the Fire, and put the Head into it, with all sorts of fine Herbs, some Leaf-Fat out of a Hogs-Belly, two Bay Leaves, Coriander and Aniseed, Cloves and Nutmeg beaten, and some Salt, if it has not been sufficiently corn’d before, add also some Onion and Rosemary: When it is half boiled, pour in a Quart of good Wine, and let it continue boiling for the Space of twelve Hours: The Tongue may also be boiled in the same Liquor: If Time will permit, the Head may be Salted, before it is dress’d, and let it lie for a while in its Brine: When it is ready, let it cool in its own Liquor; then having taken it out, let it be neatly put into a Dish and serv’d up to Table Cold, either whole or in slices.