1) In coal-mining this was the term applied to jobs done outside the particular task.
In 1671, in Halifax, advice was given about what wages the bottom-man sets down for bywork. The word figures frequently in eighteenth-century accounts: 1707 Money paid at wood for by worke from Sep. 29, Farnley
1730 all the by work in the colliery, feighing the fire pan only excepted, Swillington
1761 paid James Barker for two days bye work, Tong.