ventral segment

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. [1913 Webster]

That the probation bear no hinge, nor loop To hang a doubt on. --Shak. [1913 Webster]

2. A small, narrow opening; a loophole. [1913 Webster]

And stop all sight-holes, every loop from whence The eye of Reason may pry in upon us. --Shak. [1913 Webster]

3. A curve of any kind in the form of a loop. [1913 Webster]

4. (Telegraphy) A wire forming part of a main circuit and returning to the point from which it starts. [1913 Webster]

5. (Acoustics) The portion of a vibrating string, air column, etc., between two nodes; -- called also {ventral segment}. [1913 Webster]

{Loop knot}, a single knot tied in a doubled cord, etc. so as to leave a loop beyond the knot. See Illust. of {Knot}. [1913 Webster]