Inside, prep. or adv.
Within the sides of; in the interior; contained within; as, inside a house, book, bottle, etc.
2 other Webster entries under this spelling
Inside, a
1. Being within; included or inclosed in anything; contained; interior; internal; as, the inside passengers of a stagecoach; inside decoration. Kissing with inside lip. Shak.
2. Adapted to the interior. Inside callipers (Mech.), callipers for measuring the diameters of holes, etc. -- Inside finish (Arch.), a general term for the final work in any building necessary for its completion, but other than unusual decoration; thus, in joiner work, the doors and windows, inside shutters, door and window trimmings, paneled jams, baseboards, and sometimes flooring and stairs; in plaster work, the finishing coat, the cornices, centerpieces, etc.,; in painting, all simple painting of woodwork and plastering. -- Inside track, the inner part of a race course; hence, colloquially, advantage of place, facilities, etc., in competition.
Inside, n.
1. The part within; interior or internal portion; content. Looked he o' the inside of the paper Shak.
2. pl.
The inward parts; entrails; bowels; hence, that which is within; private thoughts and feelings. Here's none but friends; we may speak Our insides freely. Massinger.
3. An inside passenger of a coach or carriage, as distinguished from one upon the outside. [Colloq. Eng.] So down thy hill, romantic Ashbourne, glides The Derby dilly, carrying three insides. Anti-Jacobin. Patent insides or outside, a name give to newspaper sheets printed on one side with general and miscellaneous matter, and furnished wholesale to offices of small newspapers, where the blank pages are filled up with recent and local news.
Shades of meaning
Fernald lists inside only as an antonym, under boundary.
He lists it without comment; the entries above explain its neighbors.