adjective

1. corresponding in structure, position, character, etc.
2. Biol. corresponding in basic type of structure and deriving from a common primitive origin the wing of a bat and the foreleg of a mouse are homologous
3. Chem.
   1. designating or of a series of compounds each member of which has a structure differing regularly by some increment (as a CH group) from that of the adjacent members
   2. having this relation with another or other compounds of such a series
   3. designating or of a series of elements in the same group or period of the periodic table, as the halogens, actinides, etc.
4. Immunology
   1. of a serum given to and derived from the same species
   2. of a serum given to another species but for fighting the same bacterium
5. Med. homoplastic (sense )

Etymology: Gr homologos, agreeing < homos, same + legein, say: see logic