Even after all these years of looking up words, there are still plenty whose origins and history I’m unfamiliar with. Sometimes when I look one up, I nod and think “about what I expected”; sometimes I’m surprised; and sometimes I’m so taken aback that “astonished” doesn’t really cover it. This just happened to me with a word I’d been meaning to look up because I kept running across it in Ford Madox Ford’s Parade’s End, a series of novels about WWI my wife and I are currently reading. Now I learn from a Wordorigins thread that it meant “A man in charge of a bat-horse and its load; a military servant of a cavalry officer. Now generally, an officer’s servant” (“now” being 1885, when the unrevised OED entry was written), that the “bat” in both batman and bat-horse was French bât ‘pack-saddle’ (Old French bast < late Latin bastum), and that the old-fashioned pronunciation was /ˈbɑːmən/, with French-style /bɑː/! Now I want to know when the spelling pronunciation /ˈbætmən/ came into use; from the OED citations (1844 “A Bât Man is allowed to the Surgeon for the care of the horse carrying the Instruments,” where the â clearly indicates a French-style pronunciation; 1855 “The English loss was..a waggoner, three bat-men, and a horse,” where it’s ambiguous) I’d guess the mid-19th century. At any rate, by WWI I imagine only the most aged of officers still said /ˈbɑːmən/; my Daniel Jones Pronouncing Dictionary (13th ed., 1967) doesn’t even mention it, and it’s pretty careful to include obsolete forms that might still be encountered.