Definition of "adjoin"

adjoin

/əˈd͡ʒɔɪn/

verb
third-person singular simple present adjoins, present participle adjoining, simple past and past participle adjoined
1. (transitive) To be in contact or connection with.
  Quotations
  We were in the living area, which adjoins the kitchen.
  2013, Graeme Simsion, The Rosie Project, page 55
2. (transitive, mathematics, chiefly algebra and number theory) To extend an algebraic object (e.g. a field, a ring, etc.) by adding to it (an element not belonging to it) and all finite power series of (the element).