Etymology

The first citation in the Oxford English Dictionary is from a 1948 Dictionary of Forces' Slang. The OED suggests that it derives ultimately from the noun cock, but gives no further detail. ^[1] The nature of the earliest citation suggests that this expression entered the wider language from military slang, making etymologies from typesetting or archery (see below) seem unlikely.

The term is sometimes attributed to the days of manual typesetting, when a letter that had become wedged slightly higher than the other letters on the line was said to be "cocked up".

The term 'cock up' originates to medieval archery. One of the three feathers on an arrow is a cock's feather. If the arrow was incorrectly placed on the bow for drawing and release, the arrow would go off course because of the cock's feather being up and therefore the arrow positioned wrongly on the bow. This was then known as a 'cock up'.