thin edge of the wedge
A minor change that begins a major development, especially an undesirable one. For example, First they asked me to postpone my vacation for a week, and then for a month; it's the thin edge of the wedge and pretty soon it'll be a year. This term alludes to the narrow wedge inserted into a log for splitting wood. [Mid-1800s]
Nearby words
thimerosal, thimphu, thin, thin as a rail, thin client, thin edge of the wedge, thin film, thin on top, thin register, thin section, thin-film
The American Heritage® Idioms Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.