mid 17th century: from bloody. The use of bloody to add emphasis to an expression is of uncertain origin, but is thought to have a connection with the ‘bloods’ (aristocratic rowdies) of the late 17th and early 18th centuries; hence the phrase bloody drunk (= as drunk as a blood) meant ‘very drunk indeed’. After the mid 18th century until quite recently bloody used as a swear word was regarded as unprintable, probably from the mistaken belief that it implied a blasphemous reference to the blood of Christ, or that the word was an alteration of ‘by Our Lady’; hence a widespread caution in using the term even in phrases, such as bloody battle, merely referring to bloodshed.