a declaration or confirmation that someone is healthy or something is in good condition
In the mid 18th century, a bill of health was an official certificate given to the master of a ship on leaving port. If clean, it certified that there was no infection either in the port or on board the vessel.
a clean sheet = a clean sheet slate
an absence of existing restraints or commitments
2003 - Guardian - Given a clean slate and an impressive budget, I would love to programme a festival that exposed audiences to completely new forms of music making at their best and most diverse.
clean his clock
give someone a beating
defeat or surpass someone decisively - North American informal
Clock is used here in the slang sense of face.
eliminate corruption or inefficiency - North American
clean up your act
behave in a more acceptable manner – informal
be completely honest and frank – informal
have clean hands = keep your hands clean
be uninvolved and blameless with regard to an immoral act.
keep a clean sheet
(in a football match) prevent the opposing side from scoring.
keep your nose clean
stay out of trouble - Informal
make a clean breast of something = make a clean breast of it
confess your mistakes or wrongdoings.
In former times, many people believed that the breast or chest was where a person's conscience was located. The breast is still used metaphorically to represent the seat of the emotions.
make a clean sweep
remove all unwanted people or things ready to start afresh
win all of a group of similar or related sporting competitions, events or matches.
take someone to the cleaners
take all of someone's money or possessions in a dishonest or unfairway