frogyoudaoicibaDictYouDict[frog 词源字典]
frog: [OE] Frog comes from Old English frogga, which probably started life as a playful alternative to the more serious frosc or forsc. This derived from the pre-historic Germanic *fruskaz, which also produced German frosch and Dutch vorsch. Its use as a derogatory synonym for ‘French person’ goes back to the late 18th century, and was presumably inspired by the proverbial French appetite for the animals’ legs (although in fact frog as a general term of abuse can be traced back to the 14th century, and in the 17th century it was used for ‘Dutch person’).

It is not clear whether frog ‘horny wedge-shaped pad in a horse’s hoof’ [17] and frog ‘ornamental braiding’ [18] are the same word; the former may have been influenced by French fourchette and Italian forchetta, both literally ‘little fork’.
[frog etymology, frog origin, 英语词源]
frog (n.1)youdaoicibaDictYouDict
Old English frogga "frog," a diminutive of frosc, forsc, frox "frog," a common Germanic word but with different formations that are difficult to explain (cognates: Old Norse froskr, Middle Dutch vorsc, German Frosch "frog"), probably literally "hopper," from PIE root *preu- "to hop" (cognates: Sanskrit provate "hops," Russian prygat "to hop, jump"). Watkins calls the Old English -gga an "obscure expressive suffix."

The Latin word for it (rana) is imitative of croaking. Also in Middle English as frok, vrogge, frugge, and with sometimes plural form froggen. Collateral Middle English forms frude, froud are from Old Norse frauðr "frog," and native alternative form frosk "frog" survived in English dialects into the 19c.
I always eat fricasseed frogs regretfully; they remind one so much of miniature human thighs, and make one feel cannibalistic and horrid .... [H. Ellen Brown, "A Girl's Wanderings in Hungary," 1896]
As a British derogatory term for "Frenchman," 1778 (short for frog-eater), but before that (1650s) it meant "Dutch" (from frog-land "marshy land," in reference to their country). To have a frog in the throat "be hoarse" is from 1892, from frog as a name for a lump or swelling in the mouth (1650s) or throat infections causing a croaking sound.
frog (n.2)youdaoicibaDictYouDict
type of fastening for clothing, 1719, originally a belt loop for carrying a weapon, of unknown origin; perhaps from Portuguese froco, from Latin floccus "flock of wool."