What is "oblique flank"

Oblique \Ob*lique"\, a. [F., fr. L. obliquus; ob (see Ob-) + liquis oblique; cf. licinus bent upward, Gr. le`chrios slanting.] [Written also oblike.]

1. Not erect or perpendicular; neither parallel to, nor at right angles from, the base; slanting; inclined.

   It has a direction oblique to that of the former motion.
   --Cheyne.

2. Not straightforward; indirect; obscure; hence, disingenuous; underhand; perverse; sinister.

   The love we bear our friends . . . Hath in it certain oblique ends.
   --Drayton.

   This mode of oblique research, when a more direct one is denied, we find to be the only one in our power.
   --De Quincey.

   Then would be closed the restless, oblique eye. That looks for evil, like a treacherous spy.
   --Wordworth.

3. Not direct in descent; not following the line of father and son; collateral. His natural affection in a direct line was strong, in an oblique but weak. --Baker. 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.)

   1. A leaf twisted or inclined from the normal position.

   2. 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 co["o]rdinates (Anal. Geom.), a system in which the co["o]rdinate axes are oblique to each other.

n. (context fortifications English) that part of the curtain whence the fire of the opposite bastion may be discovered.