: her eager-beaver sincerity/ eager-beaver gung-ho spirit
An energetic and willing worker; ambitious striver (1940s+)
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 eager be aver
An exceptionally zealous person, one who habitually takes on more tasks or works harder than others. For example, Bill is a real eager beaver, always volunteering to stay late. This expression became especially popular during World War II, applied to recruits anxious to impress their commanding officers by such behavior.
[ First half of 1900s