The Collaborative International Dictionary of English v.0.48:
Beside \Be*side"\, prep. [OE. biside, bisiden, bisides, prep.
and adv., beside, besides; pref. be- by + side. Cf. Besides,
and see Side, n.]
1. At the side of; on one side of. "Beside him hung his bow."
2. Aside from; out of the regular course or order of; in a
state of deviation from; out of.
[You] have done enough
To put him quite beside his patience. --Shak.
3. Over and above; distinct from; in addition to.
Note: [In this use besides is now commoner.]
Wise and learned men beside those whose names are
in the Christian records. --Addison.
To be beside one's self, to be out of one's wits or senses.
Paul, thou art beside thyself. --Acts xxvi.
Syn: Beside, Besides.
Usage: These words, whether used as prepositions or adverbs,
have been considered strictly synonymous, from an
early period of our literature, and have been freely
interchanged by our best writers. There is, however, a
tendency, in present usage, to make the following
distinction between them: 1. That beside be used only
and always as a preposition, with the original meaning
"by the side of; " as, to sit beside a fountain; or
with the closely allied meaning "aside from", "apart
from", or "out of"; as, this is beside our present
purpose; to be beside one's self with joy. The
adverbial sense to be wholly transferred to the
cognate word. 2. That besides, as a preposition, take
the remaining sense "in addition to", as, besides all
this; besides the considerations here offered. "There
was a famine in the land besides the first famine."
--Gen. xxvi. 1. And that it also take the adverbial
sense of "moreover", "beyond", etc., which had been
divided between the words; as, besides, there are
other considerations which belong to this case. The
following passages may serve to illustrate this use of
Lovely Thais sits beside thee. --Dryden.
Only be patient till we have appeased
The multitude, beside themselves with fear.
It is beside my present business to enlarge on
this speculation. --Locke.
Besides this, there are persons in certain
situations who are expected to be charitable.
And, besides, the Moor
May unfold me to him; there stand I in much
That man that does not know those things which
are of necessity for him to know is but an
ignorant man, whatever he may know besides.
Note: See Moreover.
[1913 Webster] Besides