Source : Webster's Revised Unabridged Dictionary (1913)

Crenelle \Cre*nelle"\, Crenel \Cre*nel"\ (kr?-n?l"), n. [OF.
   crenel, F. cr?neau, LL. crenellus, kernellus, dim. (prob.)
   fr. L. crena notch. See {Crenny}.]
   1. An embrasure or indentation in a battlement; a loophole in
      a fortress; an indentation; a notch. See {Merlon}, and
      Illust. of {Battlement}.

   2. (Bot.) Same as {Crenature}.

Crenel \Cre*nel"\ (kr?-n?l"), n.
   See {Crenelle}.

Source : WordNet®

crenel
     n 1: one of a series of rounded projections (or the notches
          between them) formed by curves along an edge (as the
          edge of a leaf or piece of cloth or the margin of a
          shell or a shriveled red blood cell observed in a
          hypertonic solution etc.) [syn: {scallop}, {crenation},
          {crenature}, {crenelle}]
     2: a notch or open space between two merlons in a crenelated
        battlement [syn: {crenelle}]
     v : supply with battlements [syn: {crenelate}, {crenellate}]