1. Corresponding or similar in position, value, structure, or function.
2. Biology. Similar in structure and evolutionary origin, though not necessarily in function, as the flippers of a seal and the hands of a human.
3. Immunology. Relating to the correspondence between an antigen and the antibody produced in response to it.
4. Genetics. Having the same morphology and linear sequence of gene loci as another chromosome.
5. Chemistry. Belonging to or being a series of organic compounds each successive member of which differs from the preceding member by a constant increment, especially by an added CH₂ group.

[From Greek homologos, agreeing : homo-, homo- + logos, word, proportion.]

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.