side (n.)

Old English side "flanks of a person, the long part or aspect of anything," from Proto-Germanic *sīdō (source also of Old Saxon sida, Old Norse siða, Danish side, Swedish sida, Middle Dutch side, Dutch zidje, Old High German sita, German Seite), from adjective *sithas "long" (source of Old English sid "long, broad, spacious," Old Norse siðr "long, hanging down"), from PIE root *se- "long, late" (see soiree).

Original sense preserved in countryside. Figurative sense of "position or attitude of a person or set of persons in relation to another" (as in choosing sides) first recorded mid-13c. Meaning "one of the parties in a transaction" is from late 14c.; sense in a sporting contest or game is from 1690s. Meaning "music on one side of a phonograph record" is first attested 1936. Phrase side by side "close together and abreast" is recorded from c. 1200. Side-splitting "affecting with compulsive laughter" is attested by 1825.

side (v.)

late 15c., "to cut into sides" (of meat), from side (n.). Meaning "to support one of the parties in a discussion, dispute, etc.," is first attested 1590s, from side (n.) in the figurative sense; earlier to hold sides (late 15c.). Related: Sided; siding.

side (adj.)

late 14c., from side (n.).

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Definitions of side from WordNet
side (n.)
a place within a region identified relative to a center or reference location;
they always sat on the right side of the church
he never left my side
side (n.)
one of two or more contesting groups;
the Confederate side was prepared to attack
side (n.)
either the left or right half of a body;
he had a pain in his side
side (n.)
a surface forming part of the outside of an object;
he examined all sides of the crystal
Synonyms: face
side (n.)
an extended outer surface of an object;
they painted all four sides of the house
he turned the box over to examine the bottom side
side (n.)
an aspect of something (as contrasted with some other implied aspect);
he was on the heavy side
he is on the purchasing side of the business
it brought out his better side
side (n.)
a line segment forming part of the perimeter of a plane figure;
the hypotenuse of a right triangle is always the longest side
side (n.)
a family line of descent;
he gets his brains from his father's side
side (n.)
a lengthwise dressed half of an animal's carcass used for food;
Synonyms: side of meat
side (n.)
an opinion that is held in opposition to another in an argument or dispute;
there are two sides to every question
Synonyms: position
side (n.)
an elevated geological formation;
the house was built on the side of a mountain
Synonyms: slope / incline
side (n.)
(sports) the spin given to a ball by striking it on one side or releasing it with a sharp twist;
Synonyms: English
side (v.)
take sides for or against;
side (adj.)
located on a side;
the side porch
side fences