The Collaborative International Dictionary of English v.0.48:

Segment \Seg"ment\, n. [L. segmentum, fr. secare to cut, cut
   off: cf. F. segment. See Saw a cutting instrument.]
   1. One of the parts into which any body naturally separates
      or is divided; a part divided or cut off; a section; a
      portion; as, a segment of an orange; a segment of a
      compound or divided leaf.
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   2. (Geom.) A part cut off from a figure by a line or plane;
      especially, that part of a circle contained between a
      chord and an arc of that circle, or so much of the circle
      as is cut off by the chord; as, the segment acb in the
      Illustration.
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   3. (Mach.)
      (a) A piece in the form of the sector of a circle, or part
          of a ring; as, the segment of a sectional fly wheel or
          flywheel rim.
      (b) A segment gear.
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   4. (Biol.)
      (a) One of the cells or division formed by segmentation,
          as in egg cleavage or in fissiparous cell formation.
      (b) One of the divisions, rings, or joints into which many
          animal bodies are divided; a somite; a metamere; a
          somatome.
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   Segment gear, a piece for receiving or communicating
      reciprocating motion from or to a cogwheel, consisting of
      a sector of a circular gear, or ring, having cogs on the
      periphery, or face.

   Segment of a line, the part of a line contained between two
      points on it.

   Segment of a sphere, the part of a sphere cut off by a
      plane, or included between two parallel planes.

   Ventral segment. (Acoustics) See Loor, n., 5.
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The Collaborative International Dictionary of English v.0.48:

Loop \Loop\, n. [Cf. Ir. & Gael. lub loop, noose, fold, thong,
   bend, lub to bend, incline.]
   1. A fold or doubling of a thread, cord, rope, etc., through
      which another thread, cord, etc., can be passed, or which
      a hook can be hooked into; an eye, as of metal; a staple;
      a noose; a bight.
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            That the probation bear no hinge, nor loop
            To hang a doubt on.                   --Shak.
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   2. A small, narrow opening; a loophole.
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            And stop all sight-holes, every loop from whence
            The eye of Reason may pry in upon us. --Shak.
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   3. A curve of any kind in the form of a loop.
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   4. (Telegraphy) A wire forming part of a main circuit and
      returning to the point from which it starts.
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   5. (Acoustics) The portion of a vibrating string, air column,
      etc., between two nodes; -- called also ventral segment.
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   Loop knot, a single knot tied in a doubled cord, etc. so as
      to leave a loop beyond the knot. See Illust. of Knot.
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The Collaborative International Dictionary of English v.0.48:

Ventral \Ven"tral\, a. [L. ventralis, fr. venter the belly;
   perhaps akin to G. wanst: cf. F. ventral.]
   1. (Anat.) Of, pertaining to, or situated near, the belly, or
      ventral side, of an animal or of one of its parts; hemal;
      abdominal; as, the ventral fin of a fish; the ventral root
      of a spinal nerve; -- opposed to dorsal.
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   2. (Bot.)
      (a) Of or pertaining to that surface of a carpel, petal,
          etc., which faces toward the center of a flower.
      (b) Of or pertaining to the lower side or surface of a
          creeping moss or other low flowerless plant. Opposed
          to dorsal.
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   Ventral fins (Zool.), the posterior pair of fins of a fish.
      They are often situated beneath the belly, but sometimes
      beneath the throat.

   Ventral segment. (Acoustics) See Loop, n., 5.
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