noun
[ usually sing. ] an event, experience, etc. that is surprising and shows you sth that you did not already know :
Travelling around India was a real eye-opener for me.
noun
[ usually sing. ] an event, experience, etc. that is surprising and shows you sth that you did not already know :
Travelling around India was a real eye-opener for me.
Oxford Advanced Learner's English Dictionary. Оксфордский английский словарь для изучающик язык на продвинутом уровне. 2005