Crebain:

A type of bird native to Dunland, possibly some type of crow. Aragorn saw them in Hollin while travelling with the Company of the Ring, where they were obviously being used as spies by either Saruman or Sauron or both.

Cram:

The travel food of the Lake-men. Not very tasty, and very very tough.
If you want to know what cram is, I can only say that I don't know the recipe; but it is biscutish, keeps good indefinitely, is supposed to be sustaining, and is certainly not entertaining, being in fact very uninteresting except as a chewing exercise. It was made by the Lake-men for long journeys. (H.273)

Corsairs:

Many of the Corsairs were originally Black Númenoreans, who followed Sauron. The Corsairs of Umbar were a long-time scourge of Gondor, attacking the coastal towns and the harbors such as Pelargir. The sails of the ships were black and the Corsairs used slave labour, many of whom had been captured in Gondor, to aid the propulsion of their ships. Their main harbor was most likely Umbar, as they were known as "The Corsairs of Umbar". Their number was reduced by Thorongil in the later years of the Third Age and their last recorded attack was in the War of the Ring, where they were forstalled by Aragorn and the Grey Company along with the Dead Men of Dunharrow.

The Circles of the World:

The world and the heavens surrounding us.

Cirth:

The runic lettering designed by Daeron, the minstrel of Doriath during the Ages of the Stars. This form of letters was designed for inscriptions on hard materials such as stone and wood. As such, it is formed of straight lines. Though it was not especially popular among the Sindar until somewhat later, the cirth were soon in common use among the Dwarves.

These were the runes in which the inscription on the tomb of Balin was written, though they were there called Daeron's Runes by Gandalf.

This form of lettering was also called the Cirtar.

The Lord of the Rings
The Silmarillion
The Unfinished Tales
The Hobbit
The Complete Guide to Middle Earth by Robert Foster