affinity
Definitions
noun
A natural attraction or feeling of kinship to a person or thing.
A family relationship through marriage of a relative (e.g. sister-in-law), as opposed to consanguinity (e.g. sister).
A kinsman or kinswoman of a such relationship; one who is affinal.
The fact of and manner in which something is related to another.
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.
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.
Any romantic relationship.