FLY IN THE OINTMENT
This old saying comes from the Bible. In Ecclesiastes 10:1 the writer says that dead flies give perfume a bad smell (in old versions of the Bible the word for perfume is translated 'ointment').
HAT TRICK
This comes from cricket. Once a bowler who took three wickets in successive deliveries was given a new hat by his club.
HOBSONS CHOICE
This means to have no choice at all. In the 16th century and the early 17th century if you went on a journey you could hire a horse to take you from one town to another and travel using a relay of horses. (That was better than wearing out your own horse on a long journey over very poor roads). In the early 1600s Thomas Hobson was a man in Cambridge who hired out horses. However he would not let customers choose which horse they wanted to ride. Instead they had to ride whichever horse was nearest the stable entrance. So if you hired a horse from him you were given 'Hobson's choice'.
PIN MONEY
In Tudor times and before when a merchant or tradesman made a bargain it was the custom for him to give some money for the other man's wife or daughter 'for pins'. (Tudor women needed lots of pins to hold their clothes together).
RED LETTER DAYS
In the Middle Ages saints days were marked in red in calendars. People did not work on some saint's days or holy days. Our word holiday is derived from holy day.