"building where horses or cows are kept," early 13c., "building for domestic animals," from Old French estable "a stable, stall" (also applied to cowsheds and pigsties), from Latin stabulum "a stall, fold, aviary, etc." literally "a standing place," from stem of stare "to stand" (see stet).
Meaning "collection of horses belonging to one stable is attested from 1570s; transferred sense of "group of fighters under same management" is from 1897; that of "group of prostitutes working for the same employer" is from 1937.
For what the grete Stiede
Is stole, thanne he taketh hiede,
And makth the stable dore fast.
[John Gower, "Confessio Amantis," 1390]
"steadfast, firm," mid-13c., from Old French estable, from Latin stabilis "firm, steadfast," literally "able to stand," from stem of stare "to stand" (see stet). Physical sense of "secure against falling" is recorded from late 14c. Of nuclear isotopes, from 1904.