^{(1)} or·thog·o·nal Pronunciation Key (ôrthgnl)
adj.
 Relating to or composed of right angles.
 Mathematics.
 Of or relating to a matrix whose transpose equals its
inverse.
 Of or relating to a linear transformation that
preserves the length of vectors.
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
nonoverlapping or mutually independent. For example, in
architectures such as the PDP11 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). Source: Dictionary.com
Emphasis added.

