Beside means right next to somebody or something. Close enough to touch.
It is a preposition and never an adverb, so something is beside the bed but not simply beside. Take care with besides, which has an s and means in addition or apart from, and swapping the two is a very common error. There is an idiom worth knowing, since being beside yourself means being overwhelmed by emotion, usually rage or grief. Beside the point means irrelevant.
1prepositionbesideNext to or at the side of something.
“He put the glass down beside the lamp.”
Beside is simply by the side. Old English bī sīdan was two words that grew together, and besides took the same road while keeping its s.
Old English
be sīdan
Middle English
beside
English, today
beside
Built from
From Middle English beside, besiden, bisyde (also besides > besides), from Old English be sīdan, bī sīdan (“by the side (of), on the side (of)”). Compare stq biesiede (“aside”), German Low German bisied (“aside”), German beiseite (“aside, to one side”). Compare also Dutch terzijde (“aside”). by surface analysis, en + be + side.
Etymology from Wiktionary, CC BY-SA