What is a "tark"?

[Samwise]

Hm. Thanks for askin' that, Mr. Fifth, sir. I was wonderin' that myself.

Suddenly he stopped as if listening. Frodo became aware that all was very quiet, inside and outside. Gandalf crept to one side of the window. Then with a dart he sprang to the sill, and thrust a long arm out and downwards. There was a squawk, and up came Sam Gamgee's curly head hauled by one ear.