"stone or stone-like object, supposedly magical (with healing or protective power) and found in the heads of certain toads," 1550s, from toad + stone (n.). Translating Greek batrakhites, Medieval Latin bufonites; compare also French crapaudine (13c.), German krötenstein.
The Crapadine or Toadstone, we speak of before, you shall prove to be a true one, if the Toad lift himself so up against it, when it is shew'd or held to him, as if he would come at it, and leap to catch it away: he doth so much envy that Man should have that stone. ["Eighteen Books of the Secrets of Art & Nature," 1661]
"a toad, a frog," late 14c., paddok (late 12c. as a surname), probably a diminutive of pad "toad," from Old Norse padda; from Proto-Germanic *pado- "toad" (source also of Swedish padda, Danish padde, Old Frisian and Middle Dutch padde "frog, toad," also Dutch schildpad "tortoise"), of unknown origin and with no certain cognates outside Germanic. Paddock-stool was an old name for a toadstool (mid-15c.). Pad in the straw was a 16c.-17c. expression meaning "something wrong, hidden danger."
frog genus, 2010, literally "child toad," from Greek paedo- "child" (see pedo-) + phrynē typically "toad," but occasionally "frog" (the usual Greek for "frog" was batrakhos), which is perhaps from PIE root *bher- (2) "bright; brown," or else from a local pre-Greek word. It includes Paedophryne amauensis, which was formally named 2012 and is considered the world's smallest vertebrate. The amauensis is from Amau village in Papua New Guinea, near which it was first found.