The phrase to play, also to act, possum [cf. footnote] means to pretend to be dead, asleep, ignorant, etc., in order to deceive an opponent, in allusion to the opossum’s supposed habit of feigning death when threatened or attacked. William Hayne Simmons (1784-1870) mentioned this in Notices of East Florida, with an account of the Seminole Nation of Indians (Charleston, South Carolina, 1822):

We observed an opossum retreat from the side of a lake near the road, and ascend a pine tree of no great height, that grew near the bank. On coming up to the spot, it was a considerable time before we were enabled to discover where it had concealed itself; but, at length, perceived it, nestled closely in the topmost brush of the tree. My guide fired four or five times at it, without bringing it down, though he evidently hit it each time. He was, finally, compelled to give up the attempt to kill it, attributing his failure to the weakness of his powder; but, the extraordinary vivaciousness for which this animal is distinguished, was, probably, the true cause of our not getting it. After being severely wounded, they have been known to lie for several hours as if dead; and when an opportunity has occurred, have made their escape. Hence, the expression of “playing possum,” is common among the inhabitants, being applied to those who act with cunning and duplicity.

The phrase is first recorded in The battle of Eutaw Springs and evacuation of Charleston, or, The glorious 14^th of December, 1782: a national drama in five acts (Charleston, South Carolina, 1807), by William Ioor (1780-1830), who wrote:

They little thought I was playing ’Possum all the while!

and added:

Now, if I could only stumble upon proof positive, that I was the first clever fellow who saved his life by dying—split me, but I’d apply to his sapient majesty for a patent for it.

A synonymous phrase, now obsolete, was to come (the) possum over a person. In Texas and the Gulf of Mexico; or yachting in the New World (London, 1844), Matilda Houstoun (1815-1892) wrote:

The Opossum is held in great respect by the Yankees, as a particularly “smart” animal. It is very difficult to take him, and he knows an ingenious trick or two for self preservation. If he finds himself slightly wounded, and, after casting about in his mind, sees no other means of escape, he pretends to be dead, and even allows himself to be carried home and his supposed corpse to be thrown aside. Directly he finds himself alone, he starts up and makes the best of his way to the woods again. This trick of the opossum is so well known, that when a slave is suspected by his employers of shamming sickness, to avoid his work, he is compared to this cunning little beast; “Well I guess he’s coming ’possom [sic] over us.” It is difficult to deceive a Yankee, but the negroes often succeed when they pretend illness, for even as slave-owners, these people have hearts, and kind ones too.

Note: Through aphesis, possum is from opossum, from Virginia Algonquian opassom, from op-, white, and -assom, doglike animal. The opossum is an American marsupial which has a naked prehensile tail and hind feet with an opposable thumb.