before 1000;Middle English; earlier bi-siden,Old Englishbī sīdan, be sīdan; see be-, side
Can be confused
beside, besides (see usage note at the current entry)
For the prepositional meanings “over and above, in addition to” and “except” besides is preferred, especially in edited writing: Besides these honors he received a sum of money. We heard no other sound besides the breaking surf. However, beside sometimes occurs with these meanings as well.
Old English be sidan "by the side of" (only as two words), from be- + sidan dative of side (n.). By 1200, formed as one word and used as both adverb and preposition. The alternative Middle English meaning "outside" led to the sense preserved in beside oneself "out of one's wits" (late 15c.).