Old Sayings

The term "Black Mail" came from the armor used in Medieval times. The armor which was worn was called maol and it became black (as described in black market). When the two knights were dueling and one attained the upperhand, he would give the other an alternative of life or death as the sword was pointed at his face. This was known as black mailing someone.
Break a leg; knock on wood
Wish somebody extravagant success or to praise them extravagantly would attract the attention of the "evil eye", which would lead to bad luck or disaster for them. Hence, any compliment was generally followed with the Yiddish word, "kinneh-hurreh" (phonetic spelling), to ward off the "evil eye".
British Bobbies
Police force in London was established by Sir Robert Peel. For a time policemen were called 'Peelers' or 'Bobbies men'.
Cheap at half the price
"Cheap at half the price" is a way of pointing out a very low price. It's cheap, but even cheaper at half the price, therefore it's incredibly cheap. Along the same lines is "not half bad" meaning pretty good.
Cloud nine
Cloud nine is an easy one. It is of relatively recent origin. The US weather bureau listed the different cloud formations and assigned them numbers. Cumulous clouds are #9.
Cold enough to freeze the balls off a brass monkey
This saying also has roots in fact in India. The "Monkey" or brass plate to hold cannon balls was used in some on the barracks that were in colder parts of the continent, When the temperature dropped, the contracting metals would cause the pile to fall.

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