I would say no But I might have to change my mind if you can find it in a reputable source other than a typo I first found it in the Lisp 1 5 Programmer s manual there both boolean and boolian are used Searching google shows that both are in use Other two links where both spellings are used Earliest Known Uses of Some of the Words of Mathematics A catalogue and guide to the Charles S Peirce Papers boolean or Boolean I believe that the spelling of boolean should be standardized to be de capitalized when used in a sentence Example Boolean algebra simplifies circuits However they are expressed in boolean expression The word boolean appears to be derived from the person s name George Boole and just like diesel is derived from the person Rudolf Christian Karl Diesel volt from the person Volta and so on Well language isn t always as neatly regular as you might like it to be The standard usage in mathematics has a capital B therefore we use a capital B In computer science sometimes it s lowercase and that s OK too