ponyyoudaoicibaDictYouDict[pony 词源字典]
pony: [18] Latin pullus denoted a ‘young animal’, particularly a ‘young horse’ or ‘young chicken’ (it is related to English foal, and has given English pool ‘collective amount’, poultry, and pullet). From it was derived in post-classical times pullāmen, which passed into Old French as poulain ‘foal’. This had a diminutive form poulenet, and it is thought that this was the source of the early 18th-century Scottish term powny, which in due course spread southwards as pony.
=> foal, pool, poultry, pullet[pony etymology, pony origin, 英语词源]
pony (n.)youdaoicibaDictYouDict
1650s, powny, from Scottish, apparently from obsolete French poulenet "little foal" (mid-15c.), diminutive of Old French poulain "foal," from Late Latin pullanus "young of an animal," from Latin pullus "young of a horse, fowl, etc." (see foal (n.)) [Skeat's suggestion, still accepted].

German, sensibly, indicates this animal by attaching a diminutive suffix to its word for "horse," which might yield Modern English *horslet. Modern French poney is a 19c. borrowing from English. Meaning "crib of a text as a cheating aid" (1827) and "small liquor glass" (1849) both are from notion of "smallness" (the former also "something one rides"). As the name of a popular dance, it dates from 1963. The U.S. Pony Express began 1860 (and operated about 18 months before being superseded by the transcontinental telegraph). The figurative one-trick pony is 1897, American English, in reference to circus acts.
pony (v.)youdaoicibaDictYouDict
1824, in pony up "to pay," of uncertain origin. OED says from pony (n.), but not exactly how. In other sources said to be from slang use of Latin legem pone to mean "money" (first recorded 16c.), because this was the title of the Psalm for March 25, a Quarter Day and the first payday of the year (the Psalm's first line is Legem pone michi domine viam iustificacionum "Teach me, O Lord, the ways of thy statutes").