The word bloody is the adjectival form of blood but may also be used as a swear word or expletive attributive (intensifier).

Some say it may be derived from the phrase "by Our Lady", a sacrilegious invocation of the Virgin Mary. The abbreviated form "By'r Lady" is common in Shakespeare's plays around the turn of the 17th century, and interestingly Jonathan Swift about 100 years later writes both "it grows by'r Lady cold" and "it was bloody hot walking to-day" [1] suggesting that a transition from one to the other could have been under way. Others regard this explanation as dubious. Eric Partridge, in Words, Words, Words (Methuen, 1933), describes this as "phonetically implausible". Geoffrey Hughes in Swearing: A social history of foul language, oaths and profanity in English (Blackwell, 1991), points out that "by my lady" is not an adjective whereas "bloody" is, and suggests that the slang use of the term started with "bloody drunk" meaning "fired up and ready for a fight".

Another theory is that it simply comes from a reference to blood, a view that Partridge prefers. However, this overlooks the considerable strength of social and religious pressure in past centuries to avoid profanity. This resulted in the appearance of words that in some cases appear to bear little relation to their source: "Gee" for "Jesus"; "Heck" for "Hell"; "Gosh" for "God"; "dash" or "darn" for "damn". These, too, might be considered implausible etymologies if looked at only from the point of view of phonetics. Given the context in which it is used, as well as the evidence of Swift's writing, the possibility that "bloody" is also a minced oath cannot be lightly dismissed.

Although in the 1600s the word appeared to be relatively innocuous, after about 1750 it began to be considered profane in the UK and Commonwealth. The use of bloody in adult UK broadcasting aroused controversy in the 1960s and 1970s but is now unremarkable (as can be seen by the fact that in the Harry Potter movies, which are geared toward children, the character Ron says "bloody hell" many times in all three movies).

The origins of the United Kingdom's objection to "bloody" may be in part due to the connotations of Bloody Mary, most commonly referring to a particularly divisive queen of England notorious for her violent suppression of anti-Catholic views.

Bloody has always been a very common part of Australian speech and has not been considered profane for some time. The word was christened "the Australian adjective" by The Bulletin on 18 August 1894. In the 1940s an Australian divorce court judge held that "the word bloody is so common in modern parlance that it is not regarded as swearing". Meanwhile, Neville Chamberlain's government was fining Britons for using the word in public.

The word is seldom used with a negative connotation in the United States, but is sometimes used to imitate or ridicule the British. Apocryphal extensions of "bloody" are sometimes used in American humour, such as "bloody fuck" or "bloody shit", though the British rarely, if ever, use those phrases.

There is also "Bloody hell" which can mean "Damn it", or be used as a general expression of surprise.