surprisal

noun

1. (countable, obsolete, uncountable)A surprise attack or ambush; a sudden or unexpected assault.

   “Their chiefe attempts are by Stratagems, trecheries, or surprisals.”

2. (countable, obsolete, uncountable)A sudden coming-upon someone or something unexpectedly or unawares.

   “How to secure the lady from surprisal”

   “Because death is uncertain, let us prevent its surprisal.”

3. (countable, obsolete, uncountable)A surprising event or occurrence.
4. (countable, obsolete, uncountable)The feeling caused by being surprised; surprise, shock, amazement.
5. (countable, uncountable)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.