: the most important spring in a watch or clock
: the most important or powerful cause or part of something
What made you want to look up mainspring? Please tell us where you read or heard it (including the quote, if possible).
Take our visual vocab quiz
A quick quiz about stuff worth knowing
The commonly misspelled words quiz
The Vocab Quiz Game for iPhone & iPad
"Incredibly fun and addictive. And informative!" User Review, iTunes