recessive

from The American Heritage® Dictionary of the English Language, 5th Edition.

• adjective Tending to go backward or recede.
• adjective Genetics Of, relating to, or designating an allele that does not produce a characteristic effect when present with a dominant allele.
• adjective Of or relating to a trait that is expressed only when the determining allele is present in the homozygous condition.
• noun A recessive allele or trait.
• noun An organism having a recessive trait.

from The Century Dictionary.

• Tending to recede; receding; going back: used especially of accent regarded as transferred or moved backward from the end toward the beginning of a word.
• In biology, opposed to dominant, 2. See recessive, n.
• noun In biology, an organism that manifests and transmits to descendants the character which is antagonistic to a dominant, or a character which is antagonistic to a dominant character. See dominant, 2.

from the GNU version of the Collaborative International Dictionary of English.

• adjective Going back; receding.
• adjective (Genetics) Not appearing in the phenotype unless both alleles of the organism have the same trait; -- of genetic characteristics, or of the genes coding for such characteristics, in diploid organisms. Opposite of dominant.
• noun (Genetics) A genetic trait determined by a recessive{2} allele; a trait not appearing in the phenotype unless both chromosomes of the organism have the same allele; also, an allele which is recessive{2}.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective Going back; receding.
• adjective genetics Able to be covered up by a dominant trait.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• adjective (of genes) producing its characteristic phenotype only when its allele is identical
• adjective of or pertaining to a recession
• noun an allele that produces its characteristic phenotype only when its paired allele is identical