1560s, originally thieves' slang for "a horse," agent noun from prance (v.). Meaning "a prancing horse" is from 1590s.
Entries linking to prancer
prance v.
late 14c., prauncen, originally of horses in high mettle, "make a show in walking; move proudly, lifting the feet with a capering motion," a word of unknown origin. By late 14c. of persons, "to strut, swagger, act proudly and aggressively."
Perhaps related to Middle English pranken "to show off" (from Middle Dutch pronken "to strut, parade;" see prank) by influence of dance (though prank is not attested as early as this word); or perhaps from Danish dialectal prandse "to go in a stately manner." Klein suggests Old French paravancier. Related: Pranced; prancing. As a noun from 1751, from the verb.