UK, 1836—a person, country, etc., that appears powerful or threatening but is actually weak or ineffective—from Chinese ‘zhǐlǎohǔ’ (‘zhǐ’, paper, ‘lǎohǔ’, tiger)—used in the post-war years by the Chinese Communist Party of the USA and other reactionaries
UK, 1808—to make one’s beliefs or intentions plain—from the former practice of nailing an ensign to the mast of a ship, after damage during battle resulted in the ship’s colours no longer being clearly displayed, which otherwise might have been interpreted as a signal of surrender
Australia—familiar name of St Vincent’s Private Hospital, Sydney—‘Jesus’ refers to the fact that the hospital is operated by a religious organisation—‘Hilton’ alludes to the hospital’s plushness
USA, 1976—the outcome of a situation cannot be assumed—may allude to the stereotype of a large female soprano singing the final aria of an opera—from ‘church ain’t out ’till the fat lady sings’ (1976), itself from ‘church ain’t out until the singing is over’ (1872)
a representation of the letter A in scarlet cloth which Hester Prynne is condemned to wear in The Scarlet Letter (1850), by Nathaniel Hawthorne—soon came to be used figuratively in the sense of a stigma, a mark of infamy
reluctance to attend school or work, or a reduction in working efficiency, experienced on a Monday morning—UK and USA, 1908; Australia, 1910—the suffix ‘-itis’ is applied to a state of mind or tendency fancifully regarded as a disease
UK, 1710—in ease and luxury—refers to the use of clover as fodder, as explained by Samuel Johnson in A Dictionary of the English Language (1755): “To live in Clover, is to live luxuriously; clover being extremely delicious and fattening to cattle.”
dirty fingernails—1906—British and Irish English—but the comparison between the dirt edging the fingernails and the black border edging mourning paper dates back to the 19th century
dim-witted—UK, 1963—refers to the oil lamp that is symbolically lit at the beginning of the meetings of each section of the international movement Toc H