Source : Webster's Revised Unabridged Dictionary (1913)

Nopal \No"pal\, n. [Mexican nopalli.] (Bot.)
   A cactaceous plant ({Nopalea cochinellifera}), originally
   Mexican, on which the cochineal insect feeds, and from which
   it is collected. The name is sometimes given to other species
   of {Cactace[ae]}.

Source : WordNet®

nopal
     n 1: cactus having yellow flowers and purple fruits [syn: {Opuntia
          lindheimeri}]
     2: any of several cacti of the genus Nopalea resembling prickly
        pears