Heb. 'ets, meaning "a tree" (Esther 6:4), a post or gibbet. In Genesis 40:19 and Deuteronomy 21:22 the word is rendered "tree."
Source: Easton's Bible Dictionary
Gallows
GAL'LOWS, n. singular. Gallows is in the singular number and should be preceded by a, a gallows. The plural is gallowses.
1. An instrument of punishment whereon criminals are executed by hanging. It consists of two posts and a cross beam on the top, to which the criminal is suspended by a rope fastened round his neck.