orthogonal

orthogonal adj.  [from mathematics] Mutually independent;
   well separated; sometimes, irrelevant to.  Used in a generalization
   of its mathematical meaning to describe sets of primitives or
   capabilities that, like a vector basis in geometry, span the entire
   `capability space' of the system and are in some sense
   non-overlapping or mutually independent.  For example, in
   architectures such as the PDP-11 or VAX where all or nearly all
   registers can be used interchangeably in any role with respect to
   any instruction, the register set is said to be orthogonal.  Or, in
   logic, the set of operators `not' and `or' is orthogonal, but
   the set `nand', `or', and `not' is not (because any one of
   these can be expressed in terms of the others).  Also used in
   comments on human discourse: "This may be orthogonal to the
   discussion, but...."