unguessable

comparative more unguessable · superlative most unguessable

1. Not capable of being guessed.

   A woman of unguessable age, wearing lots of black clothes, snatched the child away […]

   1965, Muriel Spark, The Mandelbaum Gate, London: Macmillan, Part One, Chapter 1

   3 more examples

   Never was even washerwoman more untidy. A cap all rags, from which the hair came straggling in elf-locks over a face which generally looked red-hot, surmounted by an old bonnet, originally black, now rusty, and so twisted into crooks and bends that its pristine shape was unguessable […]

   1828, Mary Russell Mitford, “The Fisherman in his Married State”, in Our Village, London: G.B. Whittaker, page 278

   1898, Henry James, The Turn of the Screw, in The Two Magics, London: Heinemann, Chapter 13, p. 101, What it was most impossible to get rid of was the cruel idea that, whatever I had seen, Miles and Flora saw more—things terrible and unguessable and that sprang from dreadful passages of intercourse in the past.

   Especially bad are "magic words" from computer games, such as xyzzy. These magic words look secret and unguessable, but in fact they are widely known.

   2001, Simson Garfinkel, Gene Spafford, Web Security, Privacy and Commerce