What's the adjective for adjoins? Here's the word you're looking for.
Included below are past participle and present participle forms for the
verb adjoin which may be used as adjectives within certain contexts.
adjoint
(mathematics) Used in certain contexts, in each case involving a pair of transformations, one of which is, or is analogous to, conjugation (either inner automorphism or complex conjugation).
(mathematics) That is related to another functor by an adjunction.
(geometry, of one curve to another curve) Having a relationship of the nature of an adjoint (adjoint curve); sharing multiple points with.