One of the mysteries of the English language finally explained.
1A fortification or other defensive structure protecting the side of a position, body of troops, etc. Later only in plural Compare "flanker". Now historical.
2Additional or subsidiary work; specifically (informal, in a restaurant, etc.) tasks such as setting tables, polishing silverware, etc., carried out by waiting staff in addition to their main work of serving customers.
Mid 17th century. From side + work.
side work/ˈsʌɪd wəːk/
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