The Collaborative International Dictionary of English v.0.48:

Hag \Hag\ (h[a^]g), n. [OE. hagge, hegge, witch, hag, AS.
   h[ae]gtesse; akin to OHG. hagazussa, G. hexe, D. heks, Dan.
   hex, Sw. h[aum]xa. The first part of the word is prob. the
   same as E. haw, hedge, and the orig. meaning was perh., wood
   woman, wild woman. [root]12.]
   1. A witch, sorceress, or enchantress; also, a wizard. [Obs.]
      "[Silenus] that old hag." --Golding.
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   2. An ugly old woman. --Dryden.
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   3. A fury; a she-monster. --Crashaw.
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   4. (Zool.) An eel-like marine marsipobranch (Myxine
      glutinosa), allied to the lamprey. It has a suctorial
      mouth, with labial appendages, and a single pair of gill
      openings. It is the type of the order Hyperotreta.
      Called also hagfish, borer, slime eel, sucker, and
      sleepmarken.
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   5. (Zool.) The hagdon or shearwater.
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   6. An appearance of light and fire on a horse's mane or a
      man's hair. --Blount.
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   Hag moth (Zool.), a moth (Phobetron pithecium), the larva
      of which has curious side appendages, and feeds on fruit
      trees.

   Hag's tooth (Naut.), an ugly irregularity in the pattern of
      matting or pointing.
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The Collaborative International Dictionary of English v.0.48:

Borer \Bor"er\, n.
   1. One that bores; an instrument for boring.
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   2. (Zool.)
      (a) A marine, bivalve mollusk, of the genus Teredo and
          allies, which burrows in wood. See Teredo.
      (b) Any bivalve mollusk (Saxicava, Lithodomus, etc.)
          which bores into limestone and similar substances.
      (c) One of the larv[ae] of many species of insects, which
          penetrate trees, as the apple, peach, pine, etc. See
          Apple borer, under Apple.
      (d) The hagfish (Myxine).
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WordNet (r) 3.0 (2006):

borer
    n 1: a drill for penetrating rock [syn: bore bit, borer,
         rock drill, stone drill]
    2: any of various insects or larvae or mollusks that bore into
       wood [syn: woodborer, borer]