a short stretch of railroad track used to store rolling stock or enable trains on the same line to pass
"The freight train pulled into the siding to let the passenger express safely overtake it."
material applied to the outside of a building to make it weatherproof
"The carpenter installed cedar siding on the front of the house to protect it from the rain."
A building material which covers and protects the sides of a house or other building.
"The freight train pulled into the siding to let the passenger express continue without delay."
A second, relatively short length of track just to the side of a railroad track, joined to the main track by switches at one or both ends, used either for loading or unloading freight, storing trains or other rail vehicles; or to allow two trains on a same track to meet (opposite directions) or pass (same direction) (the latter sense is probably an American definition).
In plain English: A siding is an extra track of rails next to the main line that allows trains to pull off and wait without blocking traffic.
"The train slowly pulled into the siding to wait for faster traffic on the main track."
Usage: In American English, "siding" refers specifically to an auxiliary railway track or exterior wall cladding, whereas British speakers often use "side line" for the rail context. Avoid using it as a verb; if you need to describe attaching boards to a house, prefer "to side."
present participle of side
"The athlete was observed sliding down the track, his body moving swiftly along the curve."
In plain English: To side with someone means to support them and take their part during an argument or disagreement.
"The train pulled in and began siding with another passenger car on the adjacent track."
Siding comes from combining the word side with the suffix -ing, which originally meant a material or collection. The term refers to tracks running parallel to a main railway line where trains can wait without blocking traffic on the main track.