Webster's Revised Unabridged Dictionary · 1913

Besides

Besides ({not transcribed}) , adverb

[Old English Same as beside, prep.; the ending -s is an adverbial one, prop. a genitive sign.]

1.
On one side. [Obsolete] — Chaucer. Shak
2.
More than that; over and above; not included in the number, or in what has been mentioned; moreover; in addition.
The men said unto Lot, Hast thou here any besides? — Gen. xix. 12
To all beside, as much an empty shade, An Eugene living, as a Casar dead. — Pope

These sentences may be considered as elliptical.

Also: Beside

Besides ({not transcribed}) , preposition

Over and above; separate or distinct from; in addition to; other than; else than. See Beside, prep., 3, and Syn. under Beside.
Besides your cheer, you shall have sport. — Shakespeare