surprisal

(obsolete, military) A surprise attack or ambush; a sudden or unexpected assault.

(obsolete) A sudden coming-upon someone or something unexpectedly or unawares.

(obsolete) A surprising event or occurrence.

(obsolete) The feeling caused by being surprised; surprise, shock, amazement.

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.