Similar to a frog (amphibian), or to a characteristic of a frog.
Though it was not far to Jamiltepec, once outside the village, the chauffeur and his little attendant lad began to get frightened, and to go frog-like with fear.1926, D. H. Lawrence, chapter 19, in The Plumed Serpent, New York: Vintage, published 1955, page 316:
I have seen, too, a frog-like beast with protruding green eyes, which is simply a gaping mouth with a huge stomach behind it.1929, Arthur Conan Doyle, chapter 5, in The Maracot Deep:
3 more examples
a froglike croak
Parsons, Winston's fellow-tenant at Victory Mansions, was in fact threading his way across the room--a tubby, middle-sized man with fair hair and a froglike face.1949, George Orwell, Nineteen Eighty-Four, Part One, Chapter 5:
It was the typical chatter of the moment when each woman was showing off her baby, held against her froglike belly.1988, Yasunari Kawabata, “Samurai Descendant”, in Lane Dunlop, J. Martin Holman, San Francisco, transl., Palm-of-the-Hand Stories, North Point Press, page 133:
In all our adventures I do not know that I have ever seen a more strange sight than this impassive and still dignified figure crouching frog-like upon the ground and goading to a wilder exhibition of passion the maddened hound, which ramped and raged in front of him, by all manner of ingenious and calculated cruelty.1923, Arthur Conan Doyle, “The Adventure of the Creeping Man”, in The Case-Book of Sherlock Holmes, London: Murray, published 1927: