Discriminate. A companion to "don't." a manual for guidance in the use of correct words and phrases in ordinary speech, (New York: 1891.) instructed its readers
Discriminate in the use of CAPTION and HEADING. It is a perversion of the word caption
to use it in the sense of heading, although this is frequently done in the United States.
Caption means seizure or act of taking, and not headship. Don't say, “The caption of a
chapter, section, or page”; use heading. (p. 22)
In his Dictionary of Americanisms: a glossary of words and phrases, usually regarded as peculiar to the United States (1848), John Russell Bartlett explained
Caption, this legal term is used in the newspapers where an Englishman would say title, head, or heading.
On the other hand ... Merriam-Webster's Dictionary of English Usage (1995) noted
You will find few of them who object to December being used for the twelfth month, when its Latin root means 'ten,' or to manure being used as a noun meaning 'to work (land) by hand.' So when you read, for example, that caption must refer to matter above a picture because it comes from Latin caput 'head,' keep manure in mind."
In one sense there is a battle between the linguistic prescriptivists who privilege the origin of a word (etymology) in an attempt to fix its true meaning, over a description of its current usage which might be quite different from its original use, so far as that use can be traced in texts that have survived the ravages of time.
Moving on to a philosophical perspective, in his book Thinking from A to Z (Routledge 1998), Nigel Warburton provides a lucid account of the etymological fallacy, while also admitted that words bear 'vestiges' of their past use:
In terms of social media, images that do or do not bear captions are open to the play of being newly captioned, or re-captioned. The new caption, or comment, then participates in the flow of commentary, so the real-time meaning is both presenting and postponing. Does this mean that the caption is no longer a form of image seizure? Have images lost their legal entitlement? Have they been de-capitated in being captioned?
(This is starting to feel like a vertiginous whirlwind of deconstruction. I'm reminded that Derrida has been charged with merely employing the etymological fallacy ...)
But perhaps also the caption is pro-vocation; it is a call for action, for research, for critique, where image, text, and commentary, engender critical combinations and creative collisions within the spaces that they open and close. De- and/or re-territorialization of the nomadic caption?