The Collaborative International Dictionary of English v.0.48:

Oblique \Ob*lique"\, a. [F., fr. L. obliquus; ob (see Ob-) +
   liquis oblique; cf. licinus bent upward, Gr. le`chrios
   slanting.] [Written also oblike.]
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   1. Not erect or perpendicular; neither parallel to, nor at
      right angles from, the base; slanting; inclined.
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            It has a direction oblique to that of the former
            motion.                               --Cheyne.
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   2. Not straightforward; indirect; obscure; hence,
      disingenuous; underhand; perverse; sinister.
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            The love we bear our friends . . .
            Hath in it certain oblique ends.      --Drayton.
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            This mode of oblique research, when a more direct
            one is denied, we find to be the only one in our
            power.                                --De Quincey.
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            Then would be closed the restless, oblique eye.
            That looks for evil, like a treacherous spy.
                                                  --Wordworth.
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   3. Not direct in descent; not following the line of father
      and son; collateral.
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            His natural affection in a direct line was strong,
            in an oblique but weak.               --Baker.
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   Oblique angle, Oblique ascension, etc. See under Angle,
      Ascension, etc.

   Oblique arch (Arch.), an arch whose jambs are not at right
      angles with the face, and whose intrados is in consequence
      askew.

   Oblique bridge, a skew bridge. See under Bridge, n.

   Oblique case (Gram.), any case except the nominative. See
      Case, n.

   Oblique circle (Projection), a circle whose plane is
      oblique to the axis of the primitive plane.

   Oblique fire (Mil.), a fire the direction of which is not
      perpendicular to the line fired at.

   Oblique flank (Fort.), that part of the curtain whence the
      fire of the opposite bastion may be discovered. --Wilhelm.

   Oblique leaf. (Bot.)
      (a) A leaf twisted or inclined from the normal position.
      (b) A leaf having one half different from the other.

   Oblique line (Geom.), a line that, meeting or tending to
      meet another, makes oblique angles with it.

   Oblique motion (Mus.), a kind of motion or progression in
      which one part ascends or descends, while the other
      prolongs or repeats the same tone, as in the accompanying
      example.

   Oblique muscle (Anat.), a muscle acting in a direction
      oblique to the mesial plane of the body, or to the
      associated muscles; -- applied especially to two muscles
      of the eyeball.

   Oblique narration. See Oblique speech.

   Oblique planes (Dialing), planes which decline from the
      zenith, or incline toward the horizon.

   Oblique sailing (Naut.), the movement of a ship when she
      sails upon some rhumb between the four cardinal points,
      making an oblique angle with the meridian.

   Oblique speech (Rhet.), speech which is quoted indirectly,
      or in a different person from that employed by the
      original speaker.

   Oblique sphere (Astron. & Geog.), the celestial or
      terrestrial sphere when its axis is oblique to the horizon
      of the place; or as it appears to an observer at any point
      on the earth except the poles and the equator.

   Oblique step (Mil.), a step in marching, by which the
      soldier, while advancing, gradually takes ground to the
      right or left at an angle of about 25[deg]. It is not now
      practiced. --Wilhelm.

   Oblique system of coordinates (Anal. Geom.), a system in
      which the coordinate axes are oblique to each other.
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WordNet (r) 3.0 (2006):

oblique case
    n 1: any grammatical case other than the nominative [syn:
         oblique, oblique case] [ant: nominative, nominative
         case, subject case]