(aviation, travel) (in a reservation system) The letter used to signify a particular fare level.

plural of reservation booking designator

(obsolete) An ABC book; a primer.

A book containing religious prayers / (when capitalized) The Book of Common Prayer / (nautical) A small holystone

(authorship) Electronic book, a book published in electronic form.

(rare, perhaps archaic) Alternative form of bookworm

A personal notebook or journal in which memorabilia, quotations, etc., are written.

(arachnology) A lamellate respiratory organ found in arachnids.

(colloquial, with regard to income) Undeclared for tax and social insurance etc.

(theater) Able to perform scripted material from memory, without need to refer to the text. / (accounting) Off the books, not officially recorded.