Read about it...
Back
Puzzling pair: flammable/inflammable
Aug 12, 2011
Faithful reader, William Gray, asks about flammable and inflammable. I guess Gray had not yet discovered Twisty Tongue when these two words were discussed in October of 2001 and again in July of 2005. 
But this fascinating pair is worth another look.
In most linguistic courses, flammable and inflammable are used as examples of apparent opposites (antonyms) which, in fact, aren’t opposites at all. They mean exactly the same thing.
Inflammable comes from the Middle English inflamme from the Old French, inflammer. Old French lifted the word directly from the Latin flammare, flamme (to blaze; flame).
Sometimes spelled inflameable, the original 1570 meaning of inflammable was “capable of flaming.” Flammable, meaning the same thing, was first used in 1813.
We instinctively believe these words must be antonyms because of the prefix in which in many cases means “not,” for example, insufficient, inconsolable and intolerable.
Nevertheless, in often means “in” as in income, inhabit and insert.
Flammable and inflammable have caused so much confusion that the trucking industry now uses only flammable on vehicles transporting combustible goods.
Words like inflammatory, inflammation and inflame give us a better idea of the true meaning of inflammable.
Gray is also interested in the origin and usage of marshal.
My 1927 edition of the Oxford International Dictionary gives marshal’s first meaning as, “One who tends horses, especially a farrier; a shoeing smith.”
Also from 1927, The New Century Dictionary (American) puts an equine definition in first place as well — “a groom; a farrier.”
Modern dictionaries either ignore this horsey connection or consider it obsolete. Still, these old meanings give a clear indication of marshal’s origin.
We took the noun mareschal (farrier; commander) from Old French, but its origin is Late Latin and Old German. Here’s the etymology: marah (horse; mare) plus scalh (servant) from the German Schalk (knave; rogue).
Today, marshal, as a noun, often refers to a military officer holding the highest rank, as in field marshal. In British historical usage, a marshal was  a high-ranking officer or servant of the state. Marshal as an officer acting as secretary or personal assistant to a circuit judge is also British usage.
U.S. usage differs. There, a marshal is a law-enforcement officer, either federal or municipal. Or he’s the head of a police or fire department.
This word can also refer to officials who supervise sports events or who control crowds.
As a verb, we use marshal and its derivatives, such as marshalling, in reference to assembling, arranging, convening, or positioning troops, facts, or ideas — “He marshalled the ranks.”
As well, this word is used for directing on-the-ground traffic at airports.
English and U.S. spellings part company on marshal’s derivations. In the U.S., marshal carries a double l only in reference to a proper name, so our American friends write marshaled, marshaling, etc. British practice is to write marshalled, marshalling, and so on.
Although pronounced the same way, martial is unrelated to marshal. Martial is derived from the name of Mars, the Roman god of war.