colloquial shortening of tonight, attested by 1918.
Present-day student notices on bulletin boards, etc., read oftener than not, "Party Friday Nite," "Meeting Tonite," "Kum Tonite," etc. [Louise Pound, Spelling-Manipulation and Present-Day Advertising, "Dialect Notes," 1923]
Online Etymology Dictionary, © 2010 Douglas Harper
Examples from the Web for tonite
I feel most too tired to rite in you tonite, Mr. Diry, but I guess I'll tell you wot made me feel so xerted.
Tomorrer is eleckshun day, so tonite the Republercans hav been havin a gran free strete exhybishun.
Now we got to pull out of here tonite an go somewhere else like a fello tryin to sleep on a park bench."Same old Bill, eh Mable!"
One I used to hear a whole heap was ‘It goiner be a hot time in the old time tonite.’Slave Narratives: a Folk History of Slavery in the United States From Interviews with Former Slaves
Work Projects Administration
Im goin into town tonite with a bunch to eat a swell dinner on a china plate.Dere Mable