Besides, Beside, adv.
Etymology: [OE. Same as beside, prep.; the ending -s is an adverbial one, prop. a genitive sign.]
1. On one side. [Obs.] 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 Cæsar dead. Pope.
Note: These sentences may be considered as elliptical.
1 other Webster entry under this spelling
Besides, prep.
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. Shak.
Shades of meaning
Fernald has no entry of its own for besides; he lists it under also, but, yet.
Where he writes about it:
The words fall into two groups; as well as, besides, in addition, too, withal, simply add a fact or thought; also (all so), in like manner, likewise, similarly, affirm that what is added is like that to which it is added. — from also