Right, so Perhaps surprisingly is the definition — "surprisingly" is just an example of the word type we're after, and "perhaps" is the little flag telling you it's a definition by example. For the wordplay, AD gives you "notice" (as in an advert), then VER is "very" with its short tail chopped off (that's "very short"), and finally B is the usual abbreviation for "book" — bung them together, AD plus VER plus B, and you've got your answer.