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 shot in the arm, a
shot in the arm, a
A stimulus or booster, something vitalizing or encouraging, as in Getting a new concertmaster was a real shot in the arm for the orchestra. This colloquial expression alludes to a stimulant given by injection.
[ c. 1920