Wordorigins.org

Ghost is of Germanic origin. It dates back to the Old English period and the word gast. The general sense of the word is a spirit or soul and it is used in various specific contexts.

The earliest attested context is that of the soul of a dead person. From Bede’s Death-song, c.735:

Huaet his gastae godaes aeththa yflaes aefter deothdaege doemid uueorthae.
(Lo! His ghost, of good or of evil, after death-day becomes judged.)

In North America, the holiday of Halloween is chiefly celebrated by children who dress up in costume and go trick-or-treating, or begging for candy, door-to-door. The name comes from the children’s ritual greeting of trick or treat when the neighbor’s door is opened. The greeting is a bluff or threat that if candy is not forthcoming, some minor vandalism will be done to the property.

The term dates to at least 1927 when it is recorded in the Lethbridge Herald of Alberta on 4 November:

The youthful tormentors were at back door and front demanding edible plunder by the word “trick or treat” to which the inmates gladly responded and sent the robbers away rejoicing.

(Source: ADS-L)

The word Halloween is a Scottish contraction of All Hallow’s Even or All Hallow’s Eve, a reference to All Saint’s Day which falls on the first of November. October 31st is the day before, or eve of, this church holiday. The contraction dates to the 18th century when it is first recorded in the Scottish folk ballad Young Tamlane:

This night is Hallowe’en, Janet,
The morn is Hallowday.

The form All Hallow’s Eve is older, dating to at least 1556. From the Chronicle of the Grey Friars of London:

Thys yere the towne of Depe was tane...on Halhalon evyn.
(This year the town of Depe was taken...on All Hallow’s even.)

And the church holiday is even older. From Ælfric’s Grammar from c.1000:

se mónað ongynð on ealra halgena mæssedæg
(The month begins on All Hallow’s Mass-day.)

(Source: Oxford English Dictionary, 2nd Edition)

Our modern verb to be is actually a conflation of three distinct roots: es-, wes-, and beu-. The modern inflections of to be are a jumble of inflections of these three original roots. And this conflation has been going on for well over 1,200 years.

The word lewd shares a similar semantic development with the word vulgar. Both originally referred to common or ordinary people. In the case of lewd, the word originally meant lay, as in a person not in holy orders.