The Collaborative International Dictionary of English v.0.48:

Cochineal \Coch"i*neal\ (k[o^]ch"[i^]*n[=e]l; 277), [Sp.
   cochinilla, dim. from L. coccineus, coccinus, scarlet, fr.
   coccum the kermes berry, G. ko`kkos berry, especially the
   kermes insect, used to dye scarlet, as the cochineal was
   formerly supposed to be the grain or seed of a plant, and
   this word was formerly defined to be the grain of the
   Quercus coccifera; but cf. also Sp. cochinilla wood louse,
   dim. of cochina sow, akin to F. cochon pig.]
   A dyestuff consisting of the dried bodies of females of the
   Coccus cacti, an insect native in Mexico, Central America,
   etc., and found on several species of cactus, esp. Opuntia
   cochinellifera.
   [1913 Webster]

   Note: These insects are gathered from the plant, killed by
         the application of heat, and exposed to the sun to dry.
         When dried they resemble small, rough berries or seeds,
         of a brown or purple color, and form the cochineal of
         the shops, which is used for making carmine, and also
         as a red dye.
         [1913 Webster]

   Note: Cochineal contains as its essential coloring matter
         carminic acid, a purple red amorphous substance which
         yields carmine red.
         [1913 Webster]

WordNet (r) 3.0 (2006):

cochineal
    n 1: a red dyestuff consisting of dried bodies of female
         cochineal insects
    2: Mexican red scale insect that feeds on cacti; the source of a
       red dye [syn: cochineal insect, cochineal, Dactylopius
       coccus]