Q: When troops are deployed, does that mean that they were previously ployed?
A: No, we never speak of undeployed troops as “ployed”—unless we’re being humorous.
When “deploy” entered English in the 15th century, it briefly meant the same thing as the earlier word “display”—to unfold or spread out. In fact, “deploy” was merely a different way of spelling “display.”
So if either “deploy” or “display” had an etymological opposite based on the same Latin roots, it would be “ply” (to fold or layer).
Both words come ultimately from the Latin displicare, which is composed of the negative prefix dis- (un-) and plicare (fold).
This is also the ancestor of “ply,” “apply,” “comply,” “complicated,” “employ,” “imply,” “pleat,” and “splay,” according to the Oxford English Dictionary and John Ayto’s Dictionary of Word Origins.
So why did we once, very briefly, have these two words for the same thing? You might call it a printer’s idiosyncrasy.
The Latin verb displicare made its way into Old French (as desplier, later desployer), and from Old French it passed into Middle English in the 1300s as desplay (later spelled “display”).
In the late 1400s, the printer William Caxton chose to spell this word in the Parisian fashion: “deploye” and “dysploye.”
But Caxton’s variations, credited with being the first uses of “deploy,” didn’t really establish the word in English. As the OED explains, the actual adoption of “deploy” in a specific sense didn’t take place until the end of the 18th century.
That’s when “deploy” acquired its military meaning, this time adopted from the modern French déployer (unroll, unfold).
The OED defines this sense of “deploy” as “to spread out (troops) so as to form a more extended line of small depth.”
Even today, we might think of a line of “deployed” troops as being unfolded or spread out.
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