The term is conventionally credited to Emilio Mola Vidal, a Nationalist general during the Spanish Civil War (1936–39). As four of his army columns moved on Madrid, the general referred to his militant supporters within the capital as his “fifth column,” intent on undermining the loyalist government from within.
https://www.britannica.com/topic/fifth-column
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an upright pillar, typically cylindrical and made of stone or concrete, supporting an entablature, arch, or other structure or standing alone as a monument.
a vertical, roughly cylindrical thing.
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a vertical division of a page or text.
a vertical arrangement of figures or other information.
a section of a newspaper or magazine regularly devoted to a particular subject or written by a particular person.
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one or more lines of people or vehicles moving in the same direction.
"a column of tanks moved northwest"
MILITARY
a narrow-fronted deep formation of troops in successive lines.
a military force or convoy of ships.
Definitions from Oxford Languages