I. hōˈmäləjē, həˈ-, -ji noun
( -es )
Etymology: Greek homologia agreement, from homologos agreeing + -ia -y — more at homologous
1. : a similarity often attributable to common origin : affinity
the anthropologist is in the curious position of dealing with … striking homologies not necessarily due to historical contact — Edward Sapir
2.
a. : likeness short of identity in structure or function between parts of different organisms due to evolutionary differentiation from the same or a corresponding part of a remote ancestor
the structural relation between the wing of a bird and the pectoral fin of a fish is a familiar example of homology
— distinguished from analogy
b. : correspondence in structure between different parts of the same individual
3.
a. : the relation existing between chemical compounds in a series whose successive members have in composition a regular difference especially of one carbon and two hydrogen atoms CH 2 (as in the series of alcohols beginning with methyl alcohol CH 3 OH, ethyl alcohol C 2 H 5 OH, propyl alcohol C 3 H 7 OH)
b. : the relation existing among elements in the same group of the periodic table (as the elements of the halogen group)
4. : a one-to-one correspondence of two coplanar geometrical figures whereby the junction lines of correspondent points are copunctal in the center of homology and the junction points of correspondent lines are collinear on the axis of homology
II. noun
: similarity of nucleotide or amino acid sequence (as in nucleic acids or proteins)