Definition of "surprisal"

surprisal

/sə(ɹ)ˈpɹaɪzəl/

noun
countable and uncountable, plural surprisals
1. (obsolete, military) A surprise attack or ambush; a sudden or unexpected assault.
  Quotations
  Their chiefe attempts are by Stratagems, trecheries, or surprisals.
  1624, John Smith, Generall Historie, Kupperman, published 1988, page 146
2. (obsolete) A sudden coming-upon someone or something unexpectedly or unawares.
  Quotations
  How to secure the lady from surprisal
  1646 (indicated as 1645), John Milton, “Comus”, in Poems of Mr. John Milton, […], London: […] Ruth Raworth for Humphrey Mosely, […]
  Because death is uncertain, let us prevent its surprisal.
  a. 1678 (date written), Isaac Barrow, “(please specify the chapter name or sermon number). The Consideration of our Latter End”, in The Works of Dr. Isaac Barrow. […], volumes (please specify |volume=I to VII), London: A[braham] J[ohn] Valpy, […], published 1830–1831
3. (obsolete) A surprising event or occurrence.
4. (obsolete) The feeling caused by being surprised; surprise, shock, amazement.
5. An information measure as equal in bits (binary digits) to the base-2 log of 1 over the probability, with the result that the number of choices equals 2n where n is the number of bits.