111 Come clean
(PW) tell the truth
I came clean when I knew I was caught in a lie.
(MW) come clean : to tell the whole story : confess <came clean about her crimes>
(free) come clean Informal to make a revelation or confession
(usingEnglish)
If someone comes clean about something, they admit to deceit or wrongdoing.
(PhraseFinder) To make a full disclosure; to confess.
Origin
'Come clean' originated in the USA in either the late 19th or early 20th century. The earliest example that I have found of it in print is from the Moberly Evening Democrat, August 1904: "Now, then Chillicothe papers - Constitution, Democrat, Tribune - come clean. Tell the truth."
The unnamed journalist who wrote that must have liked the phrase, as it appears several times in the same paper from around that time and before I can find it elsewhere. It's possible that the phrase was coined in Moberly, but that's just conjecture.
'Come' is clearly just a shortening of 'become'; 'clean' means 'not sullied by untruth', as in the earlier phrases 'make a clean breast of it' and 'keep one's hands clean'.
(idiommeanings) come clean
(verb) to admit that something you said was untrue or that you did something wrong
Example Sentences:
Boyfriend: I love you! We’re so happy together!
Girlfriend: Yeah we are.
Boyfriend: Look, I think it’s time to come clean about something.
Girlfriend: Okay….what?
Boyfriend: I’m not actually 25.
Girlfriend: How old are you?
Boyfriend: 17.
The bad employee came clean and told his boss he had been stealing from the company.
After admitting that he was an alcoholic, Benjamin began coming clean and admitting his past mistakes.