( informal ) to involve sb/yourself in sth that is likely to be unpleasant or difficult :
I volunteered to help, and then I thought 'Oh no, what have I let myself in for!'
( informal ) to involve sb/yourself in sth that is likely to be unpleasant or difficult :
I volunteered to help, and then I thought 'Oh no, what have I let myself in for!'
Oxford Advanced Learner's English Dictionary. Оксфордский английский словарь для изучающик язык на продвинутом уровне. 2005