affinity

From Middle English affinite, from Old French affinité. Ostensibly equivalent to affine +‎ -ity.

• IPA^(key): /əˈfɪnɪti/

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affinity (countable and uncountable, plural affinities)

1. A natural attraction or feeling of kinship to a person or thing.
2. A family relationship through marriage of a relative (e.g. sister-in-law), as opposed to consanguinity (e.g. sister).
3. A kinsman or kinswoman of a such relationship; one who is affinal.
4. The fact of and manner in which something is related to another.
   • 1951 April, Stirling Everard, “A Matter of Pedigree”, in Railway Magazine, number 600, page 273:

     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.

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

     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.

5. Any romantic relationship.
6. A love interest; a paramour.
   • 1916 August, The Electrical Experimenter, New York, page 248, column 3:

     "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.

7. Any passionate love for something.
8. (taxonomy) Resemblances between biological populations, suggesting that they have a common origin, type or stock.
9. (geology) Structural resemblances between minerals; resemblances that suggest that they are of a common origin or type.
10. (chemistry) An attractive force between atoms, or groups of atoms, that contributes towards their forming bonds.
11. (medicine) The attraction between an antibody and an antigen
12. (computing) A tendency to keep a task running on the same processor in a symmetric multiprocessing operating system to reduce the frequency of cache misses.
13. (geometry) An automorphism of affine space.

• microaffinity