surprisal

English

From surprise +‎ -al.

(information measure): Defined by Myron Tribus in the 1961 book Thermostatics and Thermodynamics.

surprisal (countable and uncountable, plural surprisals)

(obsolete, military) A surprise attack or ambush; a sudden or unexpected assault. [16th–19th c.]
- 1624, John Smith, Generall Historie, Kupperman, published 1988, page 146:
  Their chiefe attempts are by Stratagems, trecheries, or surprisals.
(obsolete) A sudden coming-upon someone or something unexpectedly or unawares. [17th c.]
- 1646 (indicated as 1645), John Milton, “Comus”, in Poems of Mr. John Milton, […], London: […] Ruth Raworth for Humphrey Mosely, […], →OCLC:
  How to secure the lady from 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, →OCLC:
  Because death is uncertain, let us prevent its surprisal.
(obsolete) A surprising event or occurrence. [17th–19th c.]
(obsolete) The feeling caused by being surprised; surprise, shock, amazement. [17th–19th c.]
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.