1) A pit into which water or waste matter might flow, serving as a drain, sewer, or sump.
1524 payd the plummer ... for a synke mendyng xiiijd, York
1527 for a graytt to the seynk hede vd, York
1641 Present ... Robt Harrison Cowper for making a sinke to convey his corrupted washyngs & other offensive matter into ... the Fryaridge to his neighbours annoyance, Scarborough
1648 he doth covenante to make one sinke through the ould parlor underlinde and covered on the top with paveing and waled on the side with stone, Sowerby.
2) To excavate a vertical shaft.
The term is found in Durham as early as 1358 and it is explained with some care in The Compleat Collier
that is ‘when we sink a pit, at first we break or cut the ground four square, and the diameter of the square is generally … about 9 quarters’. As the pit was deepened, timber was used ‘in the same four square form’, until the underlying rock was reached. A Bradford lease of 1599 granted the colliers libertye for sinkeinge and diggeinge of pittes. It could be a very dangerous operation: in 1672, for instance, Robert Flowar of Sandal was sincking a coolepitt and … a great stone … fell about six yerds height upon his back. The sinker’s wages in the north-east were ‘about 12d or 14d per day’ in 1708, and the expense of sinking a pit in Birstall was fivepence per yard in 1819.