affinity

plural affinities

1. countableuncountableA natural attraction or feeling of kinship to a person or thing.

   Synonyms: kindred

2. countableuncountableA family relationship through marriage of a relative (e.g. sister-in-law), as opposed to consanguinity (e.g. sister).
3. countableuncountableA kinsman or kinswoman of a such relationship; one who is affinal.
4. countableuncountableThe fact of and manner in which something is related to another.

   A “signature” was placed on all things by God to indicate their affinities — but it was hidden, hence the search for arcane knowledge. Knowing was guessing and interpreting, not observing or demonstrating.

   1997, Chris Horrocks, “Introducing Foucault”, in The Renaissance Episteme, Totem Books, Icon Books, →ISBN, page 67

   1 more example

   There are, of course, certain differences of detail; for example, the placing of the safety valves on the boiler barrel behind the dome, which follows the practice in the Riddles 2-8-0 and 2-10-0 locomotives for the Ministry of Supply; but taken all in all, Britannia's boiler has a closer affinity with the Doncaster designs than with any other.

   1951 April, Stirling Everard, “A Matter of Pedigree”, in Railway Magazine, number 600, page 273

5. countableuncountableAny romantic relationship.
6. countableuncountableA love interest; a paramour.

   "Cut it short, sis, cut it short," he would growl at her if she started to murmur sweet "coo-coos" to her affinity stationed on the other end of the wire.

   1916 August 28, The Electrical Experimenter, New York, page 248, column 3

7. countableuncountableAny passionate love for something.
8. countableuncountablebiologyResemblances between biological populations, suggesting that they have a common origin, type or stock.
9. countableuncountablegeographyStructural resemblances between minerals; resemblances that suggest that they are of a common origin or type.
10. countableuncountablechemistryAn attractive force between atoms, or groups of atoms, that contributes towards their forming bonds.
11. countableuncountablemedicineThe attraction between an antibody and an antigen
12. countableuncountablecomputingA tendency to keep a task running on the same processor in a symmetric multiprocessing operating system to reduce the frequency of cache misses.
13. countableuncountablegeometryAn automorphism of affine space.