Are there any other Wraiths, Wights and Ghosts?

Question

Are there any examples of Wraiths, Wights or Ghosts appearing elsewhere in Tolkien's work?

Specifically, is there any mention of other ghosts/spirits that are not either the 9 Nazgûl, the Barrow-Wights or the Army Of The Dead?

Answer 1

There are many ghosts on Arda

The terms "wraith", "wight" and "ghost" are somewhat interchangeable. At least, they were not used consistently by Tolkien. Let us ignore the Ringwraiths, as they seem to be a unique case of "neither dead nor living", being tied to the Ring.

Souls without bodies

A "ghost" on Arda would be a feä ("soul") without a hroä ("body"). Normally, a feä would not just be roaming around. In the case of an Elf, it would be in the Halls of Mandos. It is unknown where the feä of Men goes.

It is important to know that once a feä becomes unhoused, Mandos only summons it to his halls. That summon can be refused. Although it was rare while Melkor and Sauron were on Arda, it seems to have become more frequent in this "age of Men":

But it would seem that in these after-days more and more of the Elves, be they of the Eldalie in origin or be they of other kinds, who linger in Middle-earth now refuse the summons of Mandos, and wander houseless in the world, unwilling to leave it and unable to inhabit it, haunting trees or springs or hidden places that once they knew.

^{The History of Middle-earth Volume 10: Morgoth's Ring, The Later Quenta Silmarillion (II), p. 223}

Houseless and Lingerers

There seems to be a difference between an Elf who "dies" and one who "fades":

On the one hand, the Houseless, rebels at least against the Rulers, and maybe even deeper under the Shadow; on the other, the Lingerers, whose bodily forms may no longer be seen by us mortals, or seen only dimly and fitfully. [...]

Moreover, the Lingerers are not houseless, though they may seem to be. They do not desire bodies, neither do they seek shelter, nor strive for mastery over body or mind.

^{The History of Middle-earth Volume 10: Morgoth's Ring, The Later Quenta Silmarillion (II), p. 224}

Thus, a Houseless would be a feä who refused the summons to the Halls of Mandos and a Lingerer would an Elf who became "shadows and memories". The Lingerers are also referred to in The Silmarillion:

In after days, when because of the triumph of Morgoth Elves and Men became estranged, as be most wished, those of the Elven-race that lived still in Middle-earth waned and faded, and Men usurped the sunlight. Then the Quendi wandered in the lonely places of the great lands and the isles, and took to the moonlight and the starlight, and to the woods and caves, becoming as shadows and memories, save those who ever and anon set sail into the West and vanished from Middle-earth.

^{The Silmarillion, Of Men, p. 117}

Communication

Not all of these ghosts are peaceful:

Some are filled with bitterness, grievance, and envy. Some were enslaved by the Dark Lord and do his work still, though he himself is gone. They will not speak truth or wisdom. To call on them is folly. To attempt to master them and to make them servants of one own's will is wickedness. Such practices are of Morgoth; and the necromancers are of the host of Sauron his servant.

^{The History of Middle-earth Volume 10: Morgoth's Ring, The Later Quenta Silmarillion (II), p. 224}

Communicating with a ghost is also dangerous, as some of them are desperately seeking a new body:

Some say that the Houseless desire bodies, though they are not willing to seek them lawfully by submission to the judgement of Mandos. The wicked among them will take bodies, if they can, unlawfully. The peril of communing with them is, therefore, not only the peril of being deluded by fantasies or lies: there is peril also of destruction.

^ibid.

Seeing an unhoused feä

Finrod does talk about seeing a feä in a discussion with Andreth:

'Men say various things, be they Wise or no,' said Andreth. 'Many hold that there is but a single thing: the body, and that we are one of the beasts, though the latest come and the most cunning. But others hold that the body is not all, but contains some other thing. For often we speak of the body as a "house", or as "raiment", and that implies an indwelling, though of what we speak in uncertainty.

'Among my folk men speak mostly of the "breath" (or the "breath of life" ), and they say that if it leaves the house, it may by seeing eyes be seen as a wraith, a shadowy image of the living thing that was.'

'That is but a guess,' said Finrod, 'and long ago we said things similar, but we know now that the Indweller is not "breath" (which the hroä uses), and that seeing eyes cannot see one that is houseless, but that the living eyes may draw from the feä within an image which the houseless conveys to the housed: the memory of itself.'

^{The History of Middle-earth Volume 10: Morgoth's Ring, Athrabeth Finrod ah Andreth, p. 352}

So it appears you can't normally see an unhoused feä unless it conveys an image of itself to you.

Gorlim

The only example I could find of a "ghost" would be Gorlim, who talked to Beren in a dream. Gorlim had been killed by Sauron earlier.

Then Beren was aware in his dream of a form that came to him across the water, and it was a wraith of Gorlim; and it spoke to him declaring his treachery and death, and bade him make haste to warn his father.

^{The Silmarillion, Of Beren and Lúthien, p. 191}

Tolkien spent some time on "communication of thought" in the Ósanwe-kenta, where he says that a combination of urgency from the sender and passivity in the receiver would make thought transmission easier:

Urgency is imparted by great need of the "sender" (as in joy, grief or fear); and if these things are in any degree shared by the "receiver" the thought is the clearer received. [...]

These causes may strengthen the thought to pass the veils and reach a recipient mind. But that mind must remain open, and at the least passive. If, being aware that it is addressed, it then closes, no urgency or affinity will enable the sender's thought to enter.

^{Ósanwe-kenta}

As Beren was sleeping and Gorlim wanted to warn him of an impending attack, this sounds probable. Although the Ósanwe-kenta only talks about housed feär, it is possible that Gorlim's feä remained in Middle-earth long enough to communicate with Beren. It may be also that Gorlim was in the Halls of Mandos at that time, since "distance in itself offers no impediment whatever to [interchange of thought]".

In any case, although this is communication with a "ghost", I could find no texts about seeing one.

Answer 2

The description of the lights in the Dead Marshes in The Two Towers, "The Passage of the Marshes", is ambiguous. It could describe will-o'-'the-wisp or the actual ghosts of those buried in the Marshes.