Corresponding
/ˌkɒɹəˈspɒndɪŋ/
verb
(constructed with to) To be equivalent or similar in character, quantity, quality, origin, structure, function etc.
(constructed with with) to exchange messages, especially by postal letter, over a period of time.
“I've been corresponding with my German pen pal for three years.”
To have sex with.
noun
A correspondence; the situation where things correspond or match.
adjective
That have a similar relationship