tree-frog (n.)

Old English treo, treow "tree" (also "timber, wood, beam, log, stake"), from Proto-Germanic *trewam (source also of Old Frisian tre, Old Saxon trio, Old Norse tre, Gothic triu "tree"), from PIE *drew-o-, suffixed variant form of root *deru- "be firm, solid, steadfast," with specialized senses "wood, tree" and derivatives referring to objects made of wood.

The line which divides trees from shrubs is largely arbitrary, and dependent upon habit rather than size, the tree having a single trunk usually unbranched for some distance above the ground, while a shrub has usually several stems from the same root and each without a proper trunk. [Century Dictionary]

In Old English and Middle English also "thing made of wood," especially the cross of the Crucifixion and a gallows (such as Tyburn tree, famous gallows outside London). Middle English also had plural treen, adjective treen (Old English treowen "of a tree, wooden"). For Dutch boom, German Baum, the usual words for "tree," see beam (n.).

Meaning "framework of a saddle" is from 1530s. Meaning "representation of familial relationships in the form of a tree" is from c. 1300. Tree-hugger, contemptuous for "environmentalist" is attested by 1989.

Minc'd Pyes do not grow upon every tree,

But search the Ovens for them, and there they be.

["Poor Robin," Almanack, 1669]

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" (if from PIE root *preu- "to hop," source also of 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 Browning, "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).

The principal inn on the island of Texel is called the Golden Frog, (de Goude kikker). We may wonder that there are not more examples of this sign in Holland, for there are, without doubt, as many frogs in that country as there are Dutchmen ; and even unto this day it is a mooted point, which of the two nations has more right to the possession of the country ; both however are of a pacific disposition, so that they live on in a perfect entente cordiale. [Larwood and Hotten, "The History of Signboards," 1866]

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.