ghost.

A disembodied soul; a soul or spirit of a deceased person; a spirit appearing after death.

Everyone believed that the ghost of an old lady haunted the crypt.

He believes in ghosts.

A spirit; a human soul.

Any faint shadowy semblance; an unsubstantial image.

not a ghost of a chance

the ghost of an idea

A false image, for example in a photographic print or negative, or on a television screen or radar display, or in a telescope, caused by poor or double reception or reflection (from a lens or screen).

A faint image that remains after an attempt to remove graffiti.

Ellipsis of ghostwriter.

I’ve written both as a ghost for experts and under my name.

A nonexistent person invented to obtain some (typically fraudulent) benefit.

A dead person whose identity is stolen by another (see ghosting).

An unresponsive user on IRC, resulting from the user's client disconnecting without notifying the server.

A copy of a file or record.

An understudy.

A covert (and deniable) agent.

An opponent in a racing game that follows a previously recorded route, allowing players to compete against previous best times.

Someone whose identity cannot be established because there are no records of such a person.

An unphysical state in a gauge theory.

A formerly nonexistent character that was at some point mistakenly encoded into a character set standard, which might have since become used opportunistically for some genuine purpose.

彁 is a ghost character from the Japanese JIS X 0208 character set.

Ellipsis of ghost pepper.

A game in which players take turns to add a letter to a possible word, trying not to complete a word.

White or pale.

ghost slug

ghost flower

Transparent or translucent.

ghost ant

ghost catfish

Abandoned.

ghost town

ghost ship

Remnant; remains.

ghost apples (a thin layer of ice in the shape of an apple, which forms around it and is left behind when the apple rots and falls out)

ghost fossils (impressions of things like shells that remain in the rock after the shell etc dissolves)

Perceived or listed but not real.

ghost cellphone vibration

ghost pain

Of a cryptid, supernatural or extraterrestrial nature.

ghost rocket

ghost deer

Substitute.

ghost writer

ghost singer

In the form be ghost: not present or involved; absent, gone.

Of a disembodied soul: to appear (somewhere or to someone) in the form of an apparition; to haunt.

To imbue (something) with a ghost-like effect or hue.

To continuously cause (someone or something) trouble; specifically, to continuously be in the thoughts of (someone) in a disturbing manner; to perturb, to trouble.

To kill (someone).

To gray out (a visual element) to indicate that it is unavailable.

To forcibly disconnect (an IRC user) who is using one's reserved nickname.

To stop communicating with (someone) on social media, through text messages, etc., without explanation, especially as a way of ending a relationship; hence, to end a relationship with (someone) by stopping all communication without explanation.

To transfer (a prisoner) to another prison, usually without first informing the prisoner.

Synonym of ghostwrite (“to write (a literary work or speech), or produce (an artistic work)), in the place of someone”); also, to carry out (an artistic performance) in the place of someone.

To appear suddenly or move like a disembodied soul; specifically (often sports); also (transitive, dated) followed by the dummy subject it: to move easily and quietly without anyone noticing; to slip.

Followed by for: synonym of ghostwrite (“to write a literary work or speech, or produce an artistic work, in the place of someone”); also, to carry out an artistic performance in the place of someone.

Of a sailing vessel: to sail seemingly with very little or no wind.

Apparently only in the writings of the Dutch-English physician Gideon Harvey (c. 1636–1640 – c. 1700–1702): to die, to expire.