The word detail is a noun that, although it’s applicable uses vary widely, is perhaps best defined as a smaller part of a larger whole. The word’s origins in the English language can be traced to the turn of the seventeenth century, when its original meaning as an ‘attention to particulars’, or ‘part by part’ sprang from the French expression en détail. This expression, formed to describe the opposite of ‘ in bulk’ or ‘wholesale’, was itself derived from the lone word détail. Usages of this word by the French can be followed still further back, even into the twelfth century. Here it was used to describe the result of the action verb ‘détailler’, itself adopted from ‘de-‘ and ‘tailler’, the former meaning ‘off of’, or ‘away from’, and the latter defined as the action of cutting into pieces. It is interesting to point out that from this final stage we can clearly see the origin of the word ‘tailor’, in the sense of one who cuts and hems fabric into clothing.
Today the term is most commonly used to describe a small portion of a physical object that may not be apparent upon immediate observation. In this sense a detail is always described by an anomaly or a difference. In the same way that a map for a physical space describes interruptions or differences in the given landscape (such as roads, fences, property lines, topography, etc), a detail could not exist if the portion it describes was not in some way separate from the larger whole encompassing it. For example, if one were to show you a swath of solid red, the fact that its composition was perfectly uniform throughout would inhibit your ability to pick out any one detail. In contrast, if you were to observe a red chesterfield you could begin to pick out smaller anomalies within the whole; for example the way the fabric folds in the places where in the factory it was trimmed too large, the manner in which the fibres of textile are laced together, or how the fabric is worn slightly at the armrests from years of a person tapping against it their ring finger while reading.
From these examples you can see also that a detail always constitutes a clue as to the events or series of events that came before it. It is for this reason that the most legendary police detectives are always portrayed as holding a magnifying glass to a hair on the floor, as not only the singular anomaly in the context of a larger picture is important, but the fact that there is almost always more detail to be seen within each detail. The same level of meaning can be superimposed on things that are not physical but perhaps more conceptual. For example the way in which a person looks down and away from when speaking with another can suggest the mental acknowledgement that they are telling a lie. In this case the detail would be the shame or conscientiousness of the speaker within the grander context of what he is saying or thinking.
"detail, n.". OED Online. September 2012. Oxford University Press. http://www.oed.com/view/Entry/51168?rskey=S7JonE&result=1&isAdvanced=false (accessed November 17, 2012).
“detail, n – Definition”. Merriam Webster Online Dictionary. November 2012. Encyclopedia Brittanica. http://www.merriam-webster.com/dictionary/detail?show=0&t=1353253195 (accessed November 17, 2012)