Adjoin, v. t. [imp. & p. p. Adjoined; p. pr. & vb. n. Adjoining.]
Etymology: [OE. ajoinen, OF. ajoindre, F. adjoindre, fr. L. adjungere; ad + jungere to join. See Join, and cf. Adjunct.]
To join or unite to; to lie contiguous to; to be in contact with; to attach; to append. Corrections . . . should be, as remarks, adjoined by way of note. Watts.
1 other Webster entry under this spelling
Adjoin, v. i.
1. To lie or be next, or in contact; to be contiguous; as, the houses adjoin. When one man's land adjoins to another's. Blackstone.
Note: The construction with to, on, or with is obsolete or obsolescent.
2. To join one's self. [Obs.] She lightly unto him adjoined side to side. Spenser.
Shades of meaning
Fernald has no entry of its own for adjoin; he lists it under add.
He lists it without comment; the entries above explain its neighbors.