marshal (n.)

c. 1200, "chief household officer;" c. 1300, "justice of the peace," from Old French conestable (12c., Modern French connétable), "steward, governor," principal officer of the Frankish king's household, from Medieval Latin conestabulus, from Late Latin comes stabuli, literally "count of the stable" (established by Theodosian Code, c. 438 C.E.), hence, "chief groom."

For first element, see count (n.1). Second element is from Latin stabulum "stable, standing place" (see stable (n.)). Probably the whole is a loan-translation of a Germanic word. Compare marshal (n.).

Meaning "an officer chosen to serve minor legal process" is from c. 1600, transferred to "police officer" by 1836. French reborrowed constable 19c. as "English police."

"female of the horse or any other equine animal," Old English meare, also mere (Mercian), myre (West Saxon), fem. of mearh "horse," from Proto-Germanic *marhijo- "female horse" (source also of Old Saxon meriha, Old Norse merr, Old Frisian merrie, Dutch merrie, Old High German meriha, German Mähre "mare"), said to be of Gaulish origin (compare Irish and Gaelic marc, Welsh march, Breton marh "horse").

The fem. form is not recorded in Gothic, and there are no known cognates beyond Germanic and Celtic, so perhaps it is a word from a substrate language. The masc. forms have disappeared in English and German except as disguised in marshal (n.). In 14c. also "a bad woman, a slut," and, apparently, also "a rabbit." As the name of a throw in wrestling, it is attested from c. 1600. Mare's nest "illusory discovery, something of apparent importance causing excitement but which turns out to be a delusion or a hoax" is from 1610s.