The Collaborative International Dictionary of English v.0.48:

Orthogonal \Or*thog"o*nal\, a. [Cf. F. orthogonal.]
   Right-angled; rectangular; as, an orthogonal intersection of
   one curve with another.
   [1913 Webster]

   Orthogonal projection. See under Orthographic.
      [1913 Webster]

WordNet (r) 3.0 (2006):

orthogonal
    adj 1: not pertinent to the matter under consideration; "an
           issue extraneous to the debate"; "the price was
           immaterial"; "mentioned several impertinent facts before
           finally coming to the point" [syn: extraneous,
           immaterial, impertinent, orthogonal]
    2: statistically unrelated
    3: having a set of mutually perpendicular axes; meeting at right
       angles; "wind and sea may displace the ship's center of
       gravity along three orthogonal axes"; "a rectangular
       Cartesian coordinate system" [syn: orthogonal,
       rectangular]

Moby Thesaurus II by Grady Ward, 1.0:

35 Moby Thesaurus words for "orthogonal":
   cube-shaped, cubed, cubic, cubiform, cuboid, diced, foursquare,
   normal, oblong, orthodiagonal, orthometric, perpendicular, plumb,
   plunging, precipitous, quadrangular, quadrate, quadriform,
   quadrilateral, rectangular, rhombic, rhomboid, right-angle,
   right-angled, right-angular, sheer, square, steep, straight-up,
   straight-up-and-down, tetragonal, tetrahedral, trapezohedral,
   trapezoid, up-and-down



The Jargon File (version 4.4.7, 29 Dec 2003):

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....?


The Free On-line Dictionary of Computing (30 December 2018):

orthogonal

    At 90 degrees (right angles).

   N mutually orthogonal vectors span an N-dimensional
   vector space, meaning that, any vector in the space can be
   expressed as a linear combination of the vectors.  This is
   true of any set of N linearly independent vectors.

   The term is used loosely to mean mutually independent or well
   separated.  It is used to describe sets of primitives or
   capabilities that, like linearly independent vectors in
   geometry, span the entire "capability space" and are in some
   sense non-overlapping or mutually independent.  For example,
   in logic, the set of operators "not" and "or" is described as
   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 loosely to mean "irrelevant to", e.g. "This may be
   orthogonal to the discussion, but ...", similar to "going off
   at a tangent".

   See also orthogonal instruction set.

   [Jargon File]

   (2002-12-02)