The Collaborative International Dictionary of English v.0.48:

Haploid \Hap"loid\ (h[a^]p"loid), a. [NL., fr. Gr. "aplo`os
   simple.] (Biol.)
   having half the number of chromosomes normally present in
   somatic cells; having only one chromosome of each type, and
   therefore having only one complete set of genes; Contrasted
   with diploid and polyploid. See also diploid.

   Note: The germ cells of animals, the ovum and sperm cells,
         are haploid, whereas the somatic cells are diploid.
         Haploid variants of somatic cells may also be generated
         under certain conditions in the laboratory.
         [PJC]

WordNet (r) 3.0 (2006):

haploid
    adj 1: of a cell or organism having a single set of chromosomes
           [syn: haploid, haploidic, monoploid] [ant:
           diploid, polyploid]
    n 1: (genetics) an organism or cell having only one complete set
         of chromosomes