From the start, immediately. For example, He said to wash the car first off, or Why wasn't she told first off? [Colloquial; late 1800s] Also see under first and foremost; first thing.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
How to use first off in a sentence
First-off we thought 'twas Lazarus coming back, but pretty soon we see 'twas a considerable smaller boat than his.Cape Cod Stories | Joseph C. Lincoln
I sure did ride fast to locate you, but your daddy wanted me to be sure to tell you, first-off, not to git skeered.The Boy from the Ranch | Frank V. Webster
But Stern, first-off, had wrenched a marble slab from the stairway.Darkness and Dawn | George Allan England