Slang definitions & phrases for under one's own steam
under one's hat
Secret; in confidence: Here it is, but it's strictly under the hat, see?(1885+)
The Dictionary of American Slang, Fourth Edition by Barbara Ann Kipfer, PhD. and Robert L. Chapman, Ph.D. Copyright (C) 2007 by HarperCollins Publishers. Cite This Source
Idioms and Phrases with under one's own steam
under one's own steam
Independently, without help, as in For two years I published the quarterly newsletter under my own steam. This expression uses steam in the sense of “driving power,” as in a steam engine.
[ Early 1900s